The Ark 2.0
Real men may not use maps, but last time I checked, they weren't guided around by floating British orbs either...
Ready a Plasma Grenade and head down yet another floor. When you get to the bottom, the door will open automatically revealing an enraged Brute Minor. Stick it to him in the crotch, and do the same to his buddy behind him. Then retreat back to the corridor and let the chaos ensue. The Arbiter and your two Marines will join in on the fight to combat the three remaining Brutes and the two pairs of shielded Jackals. Poke your head down there occasionally to join in on the fun and watch out for any stray Brute Shot rounds that may zing your way. Plasma-punch the remaining Jackals, combo-kill the Captain in the back, grab the BR ammo fro your downed Marines, and head on out the door to activate the Cartographer.
After the cut scene, duck behind one of the wall segments until the Phantom leaves, then head over to the back right corner and wait for the four Grunts to enter the platform through the far door. They will once you are instructed to head downstairs. Then pop out and headshot them. Grab a better Plasma Pistol if you need it and head back inside. Beyond those walls are four Brutes and a War Chieftain wielding a deadly Plasma Cannon. You can lure the Brutes to you one by one by shooting the locked door a few times with your Plasma Pistol. Then when they come running, simply stick them with Plasma Grenades like this...
This will work perfectly for the first three, however, the last one will remain off to the left side in one of the off sections. Wait until the Chieftain is out of view, then rush over to the side and either stick or combo kill the last Brute.
Spiral down a level to enter the Stalker room. Here you will be facing a total of four Brute Stalkers and their two Jackal companions. Though invisible, Stalkers are actually considerably easier to kill than normal Brutes. They typically don't dodge overcharged plasma or grenades, so tagging them is a cinch. You just need to steer clear of their Firebombs, and you should be fine.
Head back upstairs to where the Arbiter abandoned you, and use the camo to slip past the Chieftain unnoticed. Sneaky! Slip back outside and jump down to where the Hammer Chieftain resides. If you touched the wall like i asked you to, then the death barrier will magically be gone, and the Chieftain won't even notice your presence.
Dual wield a pair of Plasma Rifles from the nearby crate, and trade out your BR for a Carbine if you think you're low on ammo. Then retreat back to the indoors. This will trigger the six Jump-Jet Brutes to spawn along with a pair of Marksmen Jackals. Remember the two Jackals you fried in the Stalker room? Bring their Plasma Pistols outside before the door locks. By now you should have plenty of ammo to deal with the Brutes. Some will have Brute Shots. These are the real threat. Trick shoot them if you can. One or two may even boost over to your location. Normally these guys, though, will only by packing Plasma Rifles. Not a huge deal. If your shields go critical at any point, feel free to use the Invincibility to recharge them to full status.
Once you've eliminated the Brutes, only the Marksmen will remain. You should be able to headshot them from across the platform without them shooting back at all. Killing them (along with the Brutes) will mark the end of the longest, most trying mission in the campaign. The Pelican will descend from the sky and airlift you to safety. Congratulations on your monumental accomplishment!