I think the problem, IMO, is that "overrated" games are often times GOOD games actually, that maybe for whatever reason, receive a little (or alot) more attention than they really deserve.
And so people who aren't big fans resent their huge appeal and popularity, and I think out of anger or spite or frustration or whatever put the game down far more than it deserves and say its terrible or whatever as a backlash.

It's like with Halo. When Halo 2 came out, it was this gigantic global "gaming event". Even if you don't care for the series and feel there are many better FPS out there, you have people who say it "sucks" and is "terrible". Well, really, no it isn't in any justifiable way. But is it overrated?? Most would say yes.

I'm the first to admit that most of the games I find overrated are actually pretty good, but I feel they just get more attention than they probably deserve..

I just hate to see people exagerrate a game's negative points just as a backlash to the attention it gets. It's unfair.