The Ark - Refuge
Follow the army dudes along the path for quite a ways and then you they will stop behind a Covenant outpost. Use your Sniper Rifle on the big guys first, and then work your way down. Shouldn't be too hard as you will be out of their range. Collect your ammo from a canister and keep moving.
Take out any survivors and keep going until you get to the hover pad. Get up top and rip off a turret. More ammo in the canisters and then keep moving. You end up at another AA Gun. Take up a good sniping position and start again with the big Brutes and work your way down. You will have to drop your turret, but you can always pick it up later, but you probably don't need to (I didn't).
*NOTE: I hope you've realized it by now, but just in case, you don't have to waste Sniper Rifle ammo on Grunts. Grunts are no real threat when they lose their leader.*
After a while a Phantom will arrive and drop off two Hunters. You don't have a Rocket Launcher, but the same rules apply. A good strategy is to clear out all the lesser bad guys first, then let the Hunters move into the open. Then you hop down and run behind them. What you're trying to do is allow your teammates to shoot at the beasts' backs, and your friends are probably on the curved walkway. Just jump back and forth like a madman, shoot their backs with your Battle Rifle, toss a Plasma at their backs if you can, and keep doing so until they are dead.
*NOTE: You press LB to switch grenades, just FYI. You haven't needed to up to this point, but better to learn late than never.*
Now move along the path and keep fighting the enemies in your way. You don't have to do anything with this AA Gun, as you can see it's not doing anything. Enter the cave and approach a door. Go through the quick hallway to emerge back outside and gain some more friendlies.
Snipe more enemies down below, and only two of them are Brutes. Then move along the edge and toward the vehicles, but don't get in. Instead, back up to the higher ground and watch as two vehicles called Prowlers rush in. The enemies should jump out, so snipe them quickly. If they don't jump out, or if they do and then they jump back in, use the Battle Rifle to get the Brutes.
First visit the wreckage and swap your most depleted weapon for the Rocket Launcher. Now you have some choices. You can either drive or man the gun on a Prowler, or you can drive or be the gunner on a Mongoose. The Mongoose choice isn't good here because your friends don't have Rocket Launchers, but you do and you could be the gunner this time. But gunning a Prowler is the best way to go.
Whatever you do, when you start heading down the path you will jump from up high to way down below, so be ready to stick the landing. Assuming you don't crash and you avoid hitting someone, then the battle starts with enemy vehicles all around. At any time, especially if you lose a gunner, hop out and change rides. And then it's just a matter of following the path and shooting bad guys as you move.
After you make another jump you will arrive at an open area where some Choppers will drop in. Remember that if you're gunning in a Prowler, shoot where the enemy will be, not where the enemy is. Then you must go up on that bridge thing and clear both ends of enemies.
After that, backtrack a bit and take the other path. Two Ghosts will be waiting for you. Keep going and you will run into a fight between humans and Covenant. Take out the Jackals and then focus on the Ghosts when they show up. Switch vehicles if you lose your crew. In fact, it will be best if you jump out and switch to a Chopper or Ghost.
Move through the opening in the rock and there will be a Wraith to deal with. Rush to it, jump out, and tag it with a grenade. Be ready for two Ghosts to appear. It might take a while but you want to eliminate a driver and then take a Ghost, especially if you lost your other ride. Just use your Battle Rifle, backpedal, and jump around until you get a free Ghost. Get in and go over the hill to find two AA Wraiths and a bunch of other Brutes. The Wraiths are busy, so you can jump out and take that turret on the hover pad. You can use the turret as is, but you might not be able to see, so detach and handle the Brutes if you must. Then either use your Rocket Launcher on the Wraiths, or tag each with a grenade, same difference.
Now the Pelican will arrive, as will a big ship.
Forward Unto Dawn
Stand back of the big ship as it drops a whole battalion of tanks and vehicles for you to play with. Jump in the driver's seat of a Scorpion and make your way back to the wall.
*NOTE: The Scorpion's controls are different. You steer with the LS and then you move the turret with the RS. Fire with RT.*
Now comes the fun part. You will run into a few enemies on your way out of the landing area, but you can be pretty far away and still be deadly accurate. The Scorpion shells fly fast, so you can kill anything with ease. When all the rift-raft is dealth with, make your way to the hole in the rock to kill two Hunters. And when you go through the hole there will be a Phantom on the other side. Aim for the guns on it first, and then you can take it down with a few hits. Also, don't forget to take out the enemies on the ground.
Keep backtracking and keep handling the lowly Ghosts. Take out all enemies from afar if you can. When you reach the area with the door, a Phantom will drop more Wraiths. Follow the path on the left that hugs the cliff wall and take out the two Wraiths in the way. But don't stop moving, keep going to get on the bridge thing and take out the Wraith on it too. Watch out for the deadly fire of the Brutes and clear both ends of turrets.
Go to the door and allow the floating thing to open it. Get out and go through. Atop the rampway will be a piece of equipment called an Auto-Turret, so pick one up. Follow the bot down the ways and in the next area extend the bridge. There is a terminal behind this button, but its purpose and its value is beyond me. Keep moving and join up with your friends on the other side of the wall.
No, don't freak out about that Scarab, at least not at the moment. Either drive or gun the Warthog that picks you up and move along the path taking out the Ghosts that appear. Around the trail will be a small outposts of Grunts, but you can fly past them if you wish. Meet up with your team at the bottom and quickly take control of a Scorpion. Start moving and start taking out the three Wraiths firing at upon you. And then take out whatever is left.
Make your way further down the slope and then you run into the Scarab. Don't even think about getting on top of that central structure and doing something from there - doesn't work. The best thing to do is drive under the Scarab, and this time you can just stay under it for as long as you can. Focus fire on the legs and in no time the thing will fall to the ground. Then all you have to do is jump into the back of it, get up to the mid-section, rip off a turret, get to the power thing at the same spot as the last one, and blow it up. You don't get a message saying to run like last time, so after the screen starts shaking, that's a good sign to run for dear life.
Your tanks should be in good enough shape, so hop back into control of the best one and make your way up the ramp. Clear it of the enemies, but you can only take it up one level. Take out as many enemies as you can and then hop off to hoof it to the top. Regroup with your pals inside.
Real Men Don't Read Maps
There is a bit of a scene with the Oracle, and then you enter a room with more sleepers. Kill the a few and then go for the Brute, but it might take a few whacks to bring him down. Keep moving and you will hit a room that has two points of entry: top or bottom. Take the high road and use your grenades to clear the place out, or hit the Brute first and pick off the little guys with ease.
Descend and in the next narrow room will be plenty of enemies. Use grenades to clear out the big guys and then use any equipment to finish the rest off. It might get cramped and that kingly Brute will cause you grief. Use the cover all around to recharge your shields and take out all the enemies.
Keep going and you will emerge outside. Go and activate the cartographer right there in front of you. Scene, but no end level just yet.
After, follow the Oracle back inside. In the previous room is yet another big fight. Take out the Grunts as soon as you enter, then the Brutes on the left, and then the Brutes near the doors. Take the Plasma Cannon on your way out.
Down to the next room, these Brutes will use Cloaking, but they aren't that hard to see. If you see a moving outline of a Brute, shoot it. Get into the lower area and make your way to the back, where some Jackals will be waiting. But if you're running low on ammo, turn around and go find the weapon crates that will give you dual-wielding Spikers. Now take the door at the back.
*NOTE: You may have noticed a new type of grenade, the Incendiary. Just toss it to bring up small flames.*
Follow the path down and you emerge back outside. There area will have a bunch of Brutes seemingly cheering for a victory. And you'll notice a lone enemy sitting in the center. You need to eliminate that guy first. The Spikers don't really work. Your best bet is to use grenades on him and take his hammer. All I did was toss two Spike Grenades, stole his hammer, thrashed a few Brutes, and then I hid under the ramps to recharge my shield. There are plenty of places to hid, so you should be home free after you steal the hammer. Any surviving party members will also help draw the Brutes attention while you bash them. Once all is clear, it's evac time. Scene and end level.