First, let me tell you, I am a old film nut. Most movies I like are pre-21th Century.
First off, let me suggest you to watch everything in the Criterion Collection:
http://www.imdb.com/company/co0044076/
I have yet to see ANY bad movies from Criterion.
And I must confess, I didn't like Donnie Darko. It was an interesting piece but.. nothing special. I saw the director's cut btw.
And now, another confession, Superbad is one of the few movies we have turned off before the end. It didn't have a point.. it was just erm.. pointless. Yes, I'm perfectly capable of enjoing stupid, college, bad humour etc movies and enjoy them.