As for the Charlie Sheen roast itself, it was hugely inappropriate which is what roasts are supposed to be. As Whoopi Goldberg explained on The View, roasts were originally not aired and didn't include "outsiders" who could share opinions of the inappropriate jokes.
I thought the Sheen roast was really repetitive and uncreative in comparison to some of the others (Shatner, Pam Anderson). And Steve-o's repeated (twice!) runs at Mike Tyson's arm were really awkward.