Alright, now lets get this Halo poo poo out right now. I can't give the single player many props, it's pretty generic if it is still well paced. But the multiplayer I can say I enjoy, because it is one of the only games on the console that really takes user skill and makes it important. Sort of like how counterstrike and Unreal do on PC, there is a clear cut line between the good players and the bad, and it's hard to bullcrap your way into the good lineup.
But, overrated, Sonic no doubt, Resident Evil, Soul Calibur IV, GTA4 failed in terms of gameplay, but the story telling and technical feat of the city was impressive. Assassins creed is one of those games where everything sounds so kick ass and brilliant, but then it just turned into a hack and slash. The free running kicked ass and I actually really thought the fighting system nailed the whole timing aspect of hand to hand combat, but they just failed so hard in coming up with a story. But I think everyone will say that, and thus it isn't overrated. MGS4 had its moments of awesomeness, but it turned into an action shooter, and I can't forgive it for that.