THOR'S HAMMER BASE: STEALTH STRIKE

Simply, all you must do is send that sniper in on Hide and aim at whatever guys the other enemies can't see. If there are 3 of them visible, aim at the one in the back that the others aren't looking at, and then work your way towards the closest ones. The important thing is that each one you shoot at must die in 1 round. If you can't get one character to do it alone, use as many as you need, but make sure they have high Hide skills so as not to be seen. Strangely, shooting through glass does not alert nearby enemies.

All of the guys in here are worth a ton of xp, so if you haven't got the skills you want or need, you may be able to get them by the end of the mission (although, since it's the last mission, it doesn't help you much).

Perhaps the trickiest part of the level is when you reach a control room with a technician in it, near the generator room. He almost always sees you unless you go prone and crawl past his window. You can't just shoot him, because there is another guy in there that will trigger a sonic weapon that kills the whole party. Crawl past the window, go in through the door and blast the second guy first; then, take out the first one in the next round, or have someone else do it (perhaps a scout with shuriken).

Another rough part can be the scaffolding right after that area, where there are 3 guys that have crossing fields of vision. The solution to this is to take out the nearest guy and the farthest guy in the same round. The middle one will not notice for some reason.

After the scaffolding is a zone transition. Get everyone over by the door and then use it.

Now that you don't have to be 'covert', feel free to go nuts if you like on the last 3 or 4 guards. There is a locked door in here that I was unable to open (even with 141 engineering, max at level 15, + picklock set). I believe it goes downstairs to where you would be if you did the frontal assault mission. I was also unable to blow it up, even with the high-penetration heavy grenades that the guards there were carrying.

At any rate, once you open the other door that the guys were guarding, the game is over. Yay! You win.