Damon was upstaged by nearly every other major character, IMO. He just didn't come off very well as a villain. To me, at least.
And while DiCaprio's early career was sorta spotty, more recently, pretty much everything he does is pretty good. Catch Me If You Can, The Aviator, The Departed...all first class stuff. His performance in The Departed was one of the best I've ever seen, personally.
As for Bale, I think his situation's rather interesting due to his cult following. So while yeah, on this site, everyone's goo-goo for him, but at large, most people barely know who he is...so - even if he wasn't a great actor (which I believe he is) - he still wouldn't be overrated, IMO.
As for Keaton. Yeah, he's extremely underrated. His performances in Batman, Beetlejuice, Johnny Dangerously, and even Jackie Brown were all fantastic.