Oh, another one I'm sure to get hate for: Alan Rickman as Snape. I love Alan Rickman and think he's an amazing actor. I didn't think his performance as Snape was bad, he just ~wasn't~ Snape. He played him a little too flat for my taste, where book Snape is super sardonic and openly cruel.

Same for Gary Oldman as Sirius. Has nothing to do with the talent of the actor, but the actor not fitting the role.

I think for me it's just that they're both like 20-30+ years older than their book counterparts, and it's really weird and jarring.