I'm going to spoil the first fight for you:
When you kill the boss, you do a finishing move. You cut off his head. It goes flying up into the air, and blood splatters out of his head and his body. It lands back on his body, and he just kind of stands there, dead. Later during the cutscene, it turns out he's still alive. He tells you he's working on revenge against Travis, that his plan takes more than just him, and then he lifts his head off of his body, and holds it in his hand. I believe blood splatters again, and then he collapses.
The game is over-the-top with it's violence. Every boss death is similar to the one described above, but usually not as extravagant. There's blood splatter, but it's not realistic. All in all, it's cartoonish because it's so exaggerated. Aside from blood, I haven't seen any actual guts or insides, though.
Also be aware that one of the long-running jokes involve overt sexual overtones with Travis and the leading lady. And the innuendo is very, very heavy just about every time she's in a cutscene.