One quick thing before I start:
Beautiful, scenic Halo. It would make a lovely vacation spot if it weren't for the hordes of aliens bent on your destruction. Get ready to spatter their blood all over this picturesque countryside.
When you begin the level, run out, fill up on goodies, and walk over near the bridge to trigger the dropship. Your escape pod cut a swath in the ground as it crashed. Follow the line of this smoking furrow back to the river. Soon two elites and six grunts will disgorge from their dropship. You should be out of their range, but still close enough to snipe the grunts with your pistol. Some of the grunts will head straight across the bridge, so plug them before they get safely to the other side. There's plenty of ammo at the crash site, so go through as many rounds as you want. Once absolutely all the grunts are dead, we're ready to take out the elites. Two against one isn't really fair odds, so we aren't going to play fair either. We're going to get our feet a little wet and sneak around behind them. Hop into the river and head back to the waterfall. Once you're far from the keen eyes of the elites, turn right and hug the wall heading back west towards the escape pod. Keep yourself pressed against the wall until you reach the edge of the abyss, then follow the edge north out into the open in front of the escape pod. If all goes well, you should be staring at the backs of two elites who have no idea you're there. Now of course you should beat them to death. Quickly fill up your pistol, grab the secondary weapon of your choosing (I like the plasma rifle), scavenge for grenades, but don't get the health pack yet.
Cross the bridge and look out for any grunts that might have gotten through your hail of bullets. Two banshees will start making your life difficult right about now, but if you keep an eye on them and only run between cover when you're clear, they will turn around and just leave once you get far enough along. If you want to be extra thorough, use up all that assault rifle ammo on them. It will just go to waste otherwise. As you're making your way up the hill, stay relatively close to the right edge. When you're all the way up as far as the edge goes, turn left and look for a big rock against the wall to hide behind. There are four grunts and an elite frolicking in the rocks here. Peek out and snipe until all the grunts are dead, then ruthlessly slaughter the single remaining elite however you choose. A charged shot from a plasma pistol will drop his shields nicely and force him to run for cover. Don't forget the goodies back at the escape pod if you need anything at all before going on to the next area. Now you can get the health pack. After you're full, head out to save the marines.
You should get a checkpoint just before you start the next fight. Save and quit when you hit it. Checkpoints have a nasty way of creeping up in this area just after you've shot your last bullet and have no health left. If this happens, just turn the machine off and restart your game. This area is the hardest part of the level. There are six dropships that will land in rapid succession at three different landing sites. You'll get a checkpoint after you've taken out each dropship's complement of Covenant, but only save it if you've killed all the elites, most of the jackals and grunts, left the rest behind for the marines, and are already in range of the next dropship's landing site.
By the way if at any time the dropships get ahead of you and you begin to get absolutely overwhelmed, skip down past this section and read my strategy for when things get all screwed up. You can always run down the hill as well and wait around far from the action for about fifteen minutes. Foe Hammer will show up and all of the Covenant will mysteriously vanish. But that's no fun.
The first complement of troops has already engaged the marines by the time you arrive. There are two elites and two grunts on the right and four grunts on the left. Throw a frag grenade at the elites then take out the grunts on the left. They're easier to kill and they throw grenades. Throw another frag then follow up with the pistol. Hopefully, the elites on the right side will be busy with other things by now, so throw another grenade or two then clean up as necessary.
Scavenge as you run. Head immediately up the ramp over the structure, stopping to pick up the health pack and goodies at the top if you need them. Run a few feet down the ramp on the other side and drop down. Keep going and you should see the next dropship in front of you. There is some randomness to the number and type of Covenant on these dropships, but there are two elites, two jackals, and two grunts on board this one. Run to the right and approach the port (left if you're on the ship facing forward) side of the ship. As soon as the doors open, stick a plasma grenade to the elite furthest back in the ship nearest the gun. By the way plasma grenades stuck to the ship don't seem to do much, so make sure it's on the elite. If you're fast and accurate, you can stick a second to the other elite before they jump out of the ship. If not, throw another one where he'll land. Hopefully, they'll both be dead now. Toss another grenade at the jackals and move on. Don't worry about a few leftover grunts or jackals. The marines will take care of them. But grab any plasma grenades lying around.
The next landing site is past the escape pod on its right, past the pipe structure, and on a slight hill. There's a health pack on the way, but only get it if you really need it. This ship usually contains two elites and five grunts. Again the elites will come out on the port side near you, so stick plasma grenades to them or have some waiting for them when they land. Now run back to the first landing site. This is where dropship number four is touching down. Your path will take you through a pile of grunts from the other side of the dropship. Take a moment to kill any that are easy pickings and take their grenades if you're not full. Again leave the leftovers for the marines. The important thing is to keep moving.
Dropship #4 once again offers two elites and five grunts for your killing pleasure. And once again the elites will be coming out of the port side so run around the ship to the far side and stick it to them as usual. There are probably a few grenades lying around here from the first fight, so be generous with them. Hopefully there will still be some marines around to clean up after you, but even if there aren't, scavenge and move on. Paste a few grunts to the hillside on the way if they regain enough courage to attack you.
The fifth dropship lands back on the hill where number three landed. This one has three elites and four grunts. As before the elites are on the port side. Take them out as usual, but since there are three be extra generous with the grenades. If you've got a spare frag, chuck one towards the grunts. Scavenge at least one plasma grenade from the bodies then head on around to where the second dropship landed.
This is the last one. Usually it has a slightly smaller complement of nasties. Only one elite, one jackal, and four grunts. Stick a grenade to the elite then throw all you have left to kill off this group as quickly as possible.
Clean up by sniping at any surviving grunts from afar with your pistol or a needler. Use the buildings to sneak up close to (and preferably behind) any jackals that are still around and let 'em have it. Whew! If you've managed to save any marines, you rule.
Ok, now my strategy for when things get all screwed up. I can usually get to the fourth ship, but the fifth and sixth almost always require this plan. First locate a small walled-in area directly in the path of the escape pod. If it had kept sliding it would have run straight into one of its walls. There are two entrances to this place. One is very near the escape pod; the other is going to be our back door. Grab a needler if you can and head in. Once you're there, peek out the entrance towards the escape pod and snipe at grunts and jackals. Wait around for all the dropships to unload and go away while you're picking them off. You should be able to duck back in here and only very rarely will any Covenant follow or throw grenades close enough to hurt you. Once everybody is gathered, let them have it. Throw two or three grenades out at a time into their midst. Use up all your grenades and most of your pistol ammo. Keep sniping until elites are the only Covenant left. If you have a needler, use it now to hopefully reduce the number of elites. This next part requires a bit of luck. Sneak out the other entrance and run far, far away. If nobody sees you, you can now roam around freely on the other side of the main structure gathering supplies. Once you have a full needler and as many grenades as you can find, sneak back in the back way. They'll never know you left. If they do figure it out, it'll be too late. A full needler and a few grenades should do the trick, but you can always sneak out for more. Once you have cleansed the area, scavenge thoroughly then hop in the warthog for the next section. Keep your pistol and needler.
Once you're near the light bridge, you should stop back in the hall just on the edge of the enemy's visibility, where they still can't see you. There are four grunts to the left of the path and two elites, four jackals, and four grunts to the right. Kick the gunner out of his seat and lay waste to anything that moves with the chaingun. Once you're done, park your warthog back in the hall and move out towards the left where the grunts are hiding. These guys should be no problem. Snipe at them with your pistol. Move up onto the main road and look around for any jackals or grunts to snipe at on the other side of the room. Once they're gone, use up all the needles around on elites that peek out. If you're stealthy, park your warthog further in on the right and using it as a distraction sneak around the blocks in this area and take out any remaining elites from behind. If subtlety isn't your strong suit, just run them over. Any leftovers should be easy to dispose of.
To activate the light bridge, you have to hit a switch that's up a ramp near where the elites were hanging out. Park the jeep at the base of the ramp so that the gunner has a good view. This is just in case an elite tries to follow you down. Move on up the ramp. There are three elites hiding out around the corner. This is a great place to practice bouncing frag grenades off the walls. Blow them up with glee. Hit the switch and keep on truckin'.
There is an escape pod here in the open with no bodies and no Covenant around. Go ahead and grab the health pack here. One very foolish marine has left his sniper rifle here for you. You'll definitely want to pick it up to complement your pistol. This is the first sniper rifle you get in the game, and it's a real beauty.
The first group of soldiers we'll be rescuing is not the one trapped underground. Even though that's probably where you're supposed to go, we're doing things out of order so as to maximize the effectiveness of the available sniper rifles. The soldiers that get first dibs are in the area with the half-buried structure. Head northeast from the escape pod across the river and look for a tunnel. When you come into this area you should see a crashed escape pod in front of you. Bring your warthog along, but leave it in the tunnel outside the area. Make sure the gunner has a good view of the entrance though. This will be important. Near the escape pod there should be two jackals wandering around. Get used to your new sniper rifle by sending a couple of rounds through their skulls. Including these first two jackals, there are four elites, five jackals, and three grunts here. Use your sniper rifle to take them all out from a safe distance. Aim for the head of course and keep your clip topped off. Red elites will always take at least two shots. One for their shields, one for their head. Everybody else should go down with one shot to the head or a couple to the body. Stay near the entrance because a dropship will land near the escape pod when most of the enemies in this area are killed. While it's flying overhead, switch out your sniper rifle for a more up close and personal weapon, but keep track of where you dropped it. There are three elites and three grunts on board. This part is fun, but can still be tough. When the dropship empties its troops, get their attention from the entrance to this area. Grenades always work well for attracting attention. When they come after you, fall back and lure them straight into your warthog. This should severely screw these Covenant and in the confusion, you can go back into the area and mop up any enemies that run away. As long as you kept your warthog out of the area, Foe Hammer will drop off another one for you. Pick up a passenger and gunner. Head up to where the marines were camped out. There should be a brand spanking new sniper rifle there for you by one of your fallen comrades. Keep it and your pistol. Don't forget to pick up any leftover rounds in your old rifle and to snag the health pack if you need it.
Take your hogs back out into the central area. Keep them together by taking turns driving short distances and move out into the open. A couple of banshees should show up and go for the jeep you're driving. Dodge around near the other jeep and the combined fire from two chainguns should make short work of these flyboys.
Now we get to rescue the marines trapped underground. There are two entrances to where we're going. One is way up in front of the escape pod on the right; the other is a little closer behind it on the left. Go to either one, but again leave your warthogs behind before actually entering the area. You get to kill 7 elites, 7 jackals, and 8 grunts before leaving here. A few jackals and grunts are underground and won't appear until the marines are triggered. From one entrance, snipe at anything you can see. Use the pistol if you can. You don't have that many bullets for the rifle. Once you've cleared out all of the nearby Covenant, move back and go around to the other entrance. Again leave your warthogs behind. From this vantage point, you should be able to take out most of the remaining Covenant with your sniper rifle and pistol. You can even go back around to the other entrance again to snipe some more. When this area is close to empty, the marines underground will make a break for it. Switch your sniper rifle for something more practical and head underground into the fray.
Foe Hammer will come down to whisk away the survivors and bring you yet another warthog. Where does she get these things? Pick up a gunner and passenger. There's also a health pack in this area between the edge of the abyss and one of the entrances to the underground area. Don't forget to stock up before moving on.
The last group of marines is way on the other side of this whole region. It was to your right as you first drove out of the tunnel with the light bridge. This may take a while, but get all three of your hogs to the last area. There are again two entrances and it might take some exploring to find the one we're going to use. You'll have to go through a small tunnel and will end up coming out as far from the last crashed escape pod as possible. So if you go in and see some trees and a lot of space to your left and the escape pod relatively close by on your right, you're at the wrong one. Back up and go way around to your left.
Once you've found the right way in, park all three warthogs relatively close to this entrance, but out in the open enough so that they have a clear view of the area. Now comes the really fun part. Lure the Covenant back into firing range of the hogs, sit back and watch the carnage. You'll probably have to go hunt down a grunt or two, but after you kill them get back to the hogs. Dropships will start landing around them, and they will just annihilate the Covenant. Dropship after dropship will fall to their chainguns. There are four groups of Covenant that arrive not counting the ones originally here. The dropships will fire their main guns at the jeeps so try to distract them or drive the jeep they're firing at around to dodge. You don't want to lose a gunner, but of course taking their place can be loads of fun too. This last area should be a joke if you get all three warthogs in a good position. The last dropship does land rather far away, close to the crashed escape pod, so you may have to move your warthogs into a better position, but it shouldn't be a problem. Foe Hammer will soon come to take you and several thankful marines to safety. Sadly, you must now say good-bye to your fleet of jeeps. It's been fun watching so many Covenant die so quickly, but never fear. You'll get to kill many more on the Truth and Reconciliation.