In Deus Ex: Human Revolution for the PC, PS3, and Xbox 360, the first boss you encounter is Barrett, a big guy with a lot of strength augs at the end of the Fema base.
If you run in guns blazing with this guy, you’ll probably get stomped. He can take a ton of damage, he has a machine gun arm, plus tons of grenades. Especially if you’re a stealth or hacker class, it may be tough to survive this fight at first. Make sure to bring a couple different guns to this fight, there is plenty of ammo scattered around the room.
The main thing you need to do with Barrett is to kite him around the room (fight and run, fight and run), and keep pillars between the two of you. He can lose track of you fairly easily when you hide behind objects, and he moves pretty slowly, so it isn’t too hard to avoid damage once you get the hang of it.
Barrett will alternate between firing his machine gun arm at you like a madman, and throwing a spray of grenades. Keep cover when he’s shooting at you, and run like hell when he throws his grenades.
The first thing I did on this fight was hide behind the cover that’s right in front of you at the start of the fight, and toss out an EMP grenade. You get several EMP grenades throughout the FEMA base. They stun him for a moment, so use that to your advantage to run and find some better cover.
You’ll notice that there are red barrels scattered around the room. These are explosive, and it’s best to throw them at Barrett and get direct hits, then shoot him a few times while he’s stunned.
There are also some canisters around the room which have poisonous gas in them. You can toss these at him as well, but be careful because the gas sticks around for a bit and will harm you as well without the right augments to protect from it.
There are four explosive barrels in the room, so try to hit him with all four, and after some shots with a weapon while he’s stunned, he should fall.
