totally fit the band. I'd argue Metallica wouldn't have been Metallica without him. He was a very influential drummer, everyone I knew back in the 80's and early 90's thought he was great.
I'm not sure what happened. But probably a combination of not practicing, and getting out of shape. And once people found out what a pr**k he was, it was easy to hate on him. He is kind of a joke now. Even James thinks he's ridiculous, but there's probably not much he can do, Lars being a founding member just like him.