One of the best fucked up anime/manga title I've come across is Gantz. I find it to have a very interesting storyline where the protagonist deals with the change of becoming an asswipe coward, into a charismatic leader whom everyone respects (shower in a several episodes of dismemberment, fornication, flesh dissolved in acid, and you get the picture).
The plot is mental in itself, and the cast of characters give the flavor to the brew. Oh wait did I say that the lead character started as an asswipe coward turning into a charismatic leader? Now how bout this, what if he turns back into an asswipe coward? Interesting eh?
I sure as hell wouldn't want to be turned back the way I used to. Ugh.