I see a lot of people that are having problems with the bosses. I just finished the game, so here are my strats to make all the boss fights easy wins. Light spoiler, if you read ahead, you will know how many bosses there are.
First fight: This is actually the thoughest one. When the fight starts, run to your left behind the column, grab either a fire extinguisher or a green gas tube. Wait for his fire to stop and throw it at him. This will stun him, now grab all the green and red canisters from the corner and throw it at him. Then run forward and grab more stuff to thor at him. In middle difficulty he will die before he can react. If he somehow reacts, take cover behind a column, but make sure you used all the canisters around it, else he will make them explode. He will die from the canisters very quickly and you will not need to shoot once.
After you get to China, work towards the dermal EMp immunity upgrade. Its 4 points, but its worth it.
Second fight: With the EMP immunity upgrade, stand next to those computers on the walls.
Wait for her to charge you, you will be immune to the deadly attack, but it will trigger a discharge and stun her. Now go for headshots with whatever weapon you are using, an upgraded 10mm will do just fine.
2 or 3 times ad she will be done.
Optionally, you lay a concussion mine 10m or so in front of you (you get the mines right before the boss battles as free loot), it will stun her and you get headshots in. Be careful to not be in range of the mines of you dont have the vision upgrade. Also dont lay them into your retreat path.
When the fight starts, run to behind wall that is to his right and your left. after 3/4 of the length, stand still and look up. He will jump over the wall, you will be able to perform a lethal takedown on him while he in in the air. If you do it too late, he will take you down instead.
Get the typhoon implants for the next battle.
Fourth fight: Before the fight, you should have convinced the terrorist to deactivate the security system, else this fight will need heavy weapons and there wont be much clever things you can do.
When the fight starts, rush to the nearest pod, activate it and wait for it to open, once its almost open, activate typhoon. This will make you immune to all damage and take out the vessel. Run to next 2 tubes and repeat.
After it, run to the blue wall and crouch. You will be immune to the EMP and the robot should not be able to fire at you. Now you wait till the talking caught up to your actions and the wall eventually crumbles.