Final Fantasy VIII (though this is so hotly contested, I don't know how highly rated it is. The people who love it love it way too much, but the people who hate it are vehement as well.)

Metal Gear Solid. I really tried to like the series, and I want to give it more of a shot, because from what I played of The Twin Snakes I really enjoyed the story, Snake, etc. But the gameplay is just blech. I've never been one for stealth games, really.

I thought Halo was overrated until I actually played it a lot. I used to be so anti-Xbox, just like every other Nintendo fanboy. But once I'd really played the game...yeah, that was gone.