Final Fantasy VII, no question. Completely overrated simply because it was the first RPG a large majority of the US played. I can't even PLAY the game now because the graphics are so dated and the gameplay was never very good to begin with. Yes, the story is good, but honestly, when the best part about a _game_ is the _story_, there is a serious problem that needs to be fixed.
Halo is also similarly overrated for the same reason. It was the first internet/LAN-enabled first-person shooter a lot of people played. As someone who played the genre on the PC, I already knew it was fun, but there is something about the first one that you played that makes you like it more. Personally I have a rather soft spot for Quake 2, despite knowing all about the game's numerous flaws. It's the same for Halo for a lot of people.
Ocarina of Time was a 10/10 game, but it IS starting to show its age at this point. There are a few things wrong with it (Going in the menu repetitively in the Water Temple to switch boots FTL), but I wouldn't say it's overrated at all.
Personally, I still think Chrono Trigger is the best game of all time, so its obvious what my opinion on that is, but obviously, if you dislike the genre, you're probably not going to share my opinion.