I was kinda scared of the first boss fight because I read about it beforehand. And indeed, it ended my five hours or so gaming session after about 20-30 tries and dying very fast in frustratrion.
But the boss fights are ridiculously easy. With typhoon, they are even more easy. There's just some things you need to know about each boss. All bosses can be stunned with the stun gun, which helps a lot.
For the first boss, you stun him and then run around throwing every barrel at your disposal at him, and he will go down.
The second boss gets stunned and just gunned down or killed with the help of the generators at the side. Also, this is pretty much the only occasion where the Track'n'mark aug is useful, because you know exactly where she is when she is stealthed. She can easily go down in a few seconds.
The last boss requires some more shooting and hiding behind columns. But he also can be killed in a few seconds with a takedown if you time it right (you need to takedown him right after he jumps over the wall and I think it must be while he is in midair or he will counter... it's on YouTube somewhere