Greetings, gentlemen. I have heard that quite a few of you have trouble with the bosses in the new Deus Ex. So had I and I cursed a lot. They are the worst part of an otherwise great game and you shouldn't let them ruin your fun. I originally wrote this for a friend but I figured I might as well put an extended and actually readable version up here.
Human Revolution is a lot like the first Deus Ex when it comes to weapons. Lots of fancy guns but most of them are either too weak, too wasteful, too big or any combination thereof.
10mm Pistol: In regular gameplay, absolutely overpowered - mainly because of the armor piercing upgrade. I'm not quite sure how armor piercing affects bosses but it just doesn't have the raw damage output that other weapons have. Don't bring a scalpel to a knife fight.
Combat Rifle: In most shooters, the assault rifle is your bread-and-butter gun. Here, not so much. Once the first armored enemies appear, it loses its punch and you'll only ever use it if you run out of pistol ammo.
Shotgun: Pretty much the same as the Combat Rifle. The damage output is okay but the short effective range is just too crippling.
Machine Pistol: Combining the worst qualities of the pistol and the Combat Rifle. Don't bother.
Crossbow: Terrible all around.
Sniper Rifle: Outclassed by the Tranquilizer Rifle in regular gameplay. You simply don't have enough space to use it effectively in boss battles.
Rocket Launcher: Very underwhelming. It's plain overkill for regular gameplay, too large to keep it for boss battles and in the end, it doesn't achieve much more than a frag nade.
Heavy Rifle: Great weapon with enormous damage output. The better Combat Rifle.
Revolver: If the 10mm is a scalpel then this gun is a chainsaw. It's basically a cross between the Sniper Rifle and the Shotgun and generally the best weapon for everything that doesn't die from a pistol headshot. This is where you want to put your upgrades.
Laser Rifle: Absolute gamebreaker. Pretty much an improved Heavy Rifle. That can shoot through walls. Requires the Smart Vision aug to shine.
Plasma Rifle: The last and the worst weapon.
Stun Gun: You can stunlock the first two bosses to death with this but it will take about 25-30 shots. Otherwise it will just stun them like an EMP nade.
Tranquilizer Rifle: Doesn't seem to have any effect on bosses.
I played through on the highest difficulty without any of the combat orientated augmentations. The Typhoon aug is incredibly powerful and fully upgraded does seem to do twice the damage of a frag nade. The damage reduction aug keeps you alive a lot longer and the EMP shield is also very useful. The recoil reduction augs barely matter but it's nice to have them anyway.
First boss battle
Not too hard, really. You should use the revolver for this fight. His weapon seems to be identical to a Heavy Rifle and he can also hurl frag nades at you. Additional, he can grab you, which hurts a lot.
Start out throwing a grenade of your own. Don't go left, you won't be able to escape from there. Either use the barricade in front of you or one of the pillars as cover and headshot him with the revolver. Keep your distance and watch out for more nades of his. Either throw the barrels directly at him or shoot them when he is near them. He should go down within a reasonable amount of time. If you keep getting killed, try spamming nades.
Second boss battle
You really want to have the EMP shield for this. She starts out charging at you. Jump immediately left or right to avoid the blast radius. She's a lot more agile than the first boss but her dual MPs hurt not quite as much. Also, she will be cloaked for most of the fight but that's not much of a problem. The water will reveal her movement as will the Smart Vision aug.
Either use the Revolver or the Heavy Rifle (you find one in the last room before the boss arena), move backwards and shot whenever she appears. Lay out mines, if you have any.
There is also a trick to this. Whenever you shoot those large panels at the wall, they will emit an electric burst that will apply the effect of an EMP nade to everything in front of it. That can hurt you just as much as it hurts her but the EMP shield protects you. It's really hard to not take any damage in this fight so have at least some meds ready.
Third boss battle
If you have the Laser Rifle, the Smart Vision augmentation and not accepted the chip exchange back in Shanghai, you have already won. He cannot shoot through walls, you can. About a full clip of the Laser Rifle will kill him.
If you are a poor fool like me, you will have a Shotgun as your only lethal weapon, exchanged the chip and additionally play on the highest difficulty, you are pretty much screwed. Exchanging the chip will not only disable all your augmentations for this fight (besides regeneration) but it will also apply the EMP effect throughout it so you have no way of knowing how much health you have at the moment or how many rounds you have in your weapon. You can still use meds from your inventory.
He is cloaked most of the time like the second boss but additionally jumps around and if he appears in front of you, you are as good as dead. His Plasma Rifle kills you almost instantly. Additionally, he somehow can throw two grenades at once. The only way to defeat him in a straight firefight and the exchanged chip is either savescumming or cornering him with grenades (which is how I did it).
Fourth boss battle
Easy as pie. Take out the turrets first. After that, push the buttons and kill the drones. At that time she will release a couple of zombies as well as small security robots. Not much of a challenge. Additionally, the floor will emit electric bursts at times but the EMP shield will negate it. Either hack the consoles or enter the password, then open the door and kill Zhao. The end.