Oh yeah, the sex scenes in Girls are pretty rough. But I would say that the show has improved as it's continued.
Although the characters are often shown in unflattering ways, I don't think it's right to say that they have no redeeming values. Even Adam, in the last couple of episodes, has become weirdly sympathetic. They're young - they act like jerks sometimes! This is realism! Besides, at this point in the show, I think pretty much every character has been called to account for their bad behavior, so we can be pretty sure that the show is not an uncritical portrayal of these characters.
And even if that weren't true, there are lots and lots of other comedies that everyone loves which have nasty/idiotic/self-involved lead characters: Eastbound and Down, Seinfeld, It's Always Sunny in Philadelphia, the Larry Sanders Show...
edit: Having written all this, I realize that there isn't exactly a shortage of Girls-related commentary on the internet. So forgive me! But I think this is one of the best things on tv these days.
