Super Mario Sunshine as a successor to Mario 64. What the hell was THAT?! I was almost offended at how bad it was.

And I have to just say that the most unexpectedly GOOD sequel for me was FFX-2, contrary to popular opinion. It looked so bad it was scary, and I always thought FFX was a generally forgettable game in the first place. I had no intention of playing it, but it was forced upon me and I'm pretty grateful for that. I think I even liked it better than FFX. The story was nothing amazing, and sometimes the dialogue made me cringe. But it was FUN.