Well I've only beaten it three times. Once on normal, once on hard and once on extreme (we had a stupid aimbotter in the room for that though.)
The best advice is to work as a team. Have a good set of teammates. Preferably your clan, or play on Echo, or Kilo server if possible. Please don't be an asshole who drops out of the room if they die in the first alley or the temple. So many times I've made it to the last objective and only had for or five teammates because of that.
For that first little alley before you reach the temple, basically if everybody rushes it or just a few going methodically works. As for the temple, kill EVERYONE before you open the gates. This way you don't have to fight enemies next to you AND above you. Once you get to the upper floor you know the drill. One guy rushes and drops a grenade, then runs back and you try to just wait it out until they stop respawning.
If you you see everybody throw their nades, HOLD ONTO YOURS!! This way if you're the last one left you can chuck it in the room without taking too much, or any damage. Once you're past the temple, have two or three people rush to the tank, while the team clears the rest of our terrorist friends. Once they get regrouped, blow up the tank. One person hop in the tank (trust me, the fire won't kill you,) someone hop on the bus, and the rest provide support fire, or take their spot if they're out of ammo. Now we're to the last part. Clear all the spots that are immediately around you. Now have two people stay back. The rest of the team get to the objective, whichever that may be. By the time they clear that, there should only maybe be two or three surviving (most likely they have low health.) Once they get there, the two at the starting point get into the action. As soon as you collect the intel, enemies spawn from where you started off in the level and meet you straight on. This is the entire reason to have people hang back. This way you can kill them from both sides (see Germany 1939-1945 lol.) Everyone then move to the "escape area" and you're done. Hopefully you'll have a nade on you. You'll need it.
To recap:
- Use your brains
- Don't drop out early
- Think logically
- Conserve ammo
- Oh, don't try using gases... I've seen people try flash grenades and blind themselves. It's good for a laugh though.
- Use cover
- Scope your weps
- You're not Rambo, so don't try to go crazy
- Have a good team
- If all else fails, have an aimbotter I guess lol