Honestly, his roles really didn't start to become interesting until Catch Me If You Can. Everything before that just bores the hell out of me. I'm not a fan of Gilbert Grape, but then again, I loathe Depp.
I like older and more experience Leo. (Sorry fangirls and boys) So I think he's acting was horrid back in the day but he has really proven himself. I liked him a lot in The Departed, Body of Lies, and R. Road. Really anything after Gangs of New York is a sure win with him.