Okay... bossfights in this game can be nigh freakin' impossible if you don't come well prepared. Been getting my bullet-riddled and charbroiled-by-electricity ass handed to me fairly consistently by one of the bosses. I think I've figured the fight out, though. It'll be hard to pull off without certain augs I've now realized are very valuable, but I'll manage, I think.
Don't fall into the same trap I did. Keep yourself well stocked and don't let yourself run low on useful stuff like painkillers, ammo and so on. There's usually enough ammo/stuff available during the bossfight itself, but if you've specialized yourself in various ways, the supplies may not be all that useful to your particular 'build' and preference. I've basically found that my personal build and preference is almost overpowered for the average gameplay, but suffers when facing the bosses.
It speaks well for the game, though, that I actually grin and enjoy the fact that you can gimp yourself for certain encounters and so on. It makes things very challenging, sure, but it also makes it so much more fun.