I agree with Resident Evil, I loved the first two (not saying they're great, just that I loved them).
I would also have to say Pirates of the Carribean, because the first one was great. The second and third ones were also, however, very very enjoyable, and on the end note of the third one I thought they'd be done.. Then the fourth one came out, and though it was still decent, I was wondering if they would ever stop. They have plans for a fifth one now.
I think everyone is going to say Star Wars, and I'd be lying if I said I didn't agree. They're not terrible, and I am actually excited to see what Disney will be able to do with the series, but again, Disney has been known to keep things going for longer than they should. SO many unnecessary sequels.