I actually change my statement, I think Halo is just fine rated. It's definetly not overrated due to the fact that people who never played it hate it as some kind of fad or something.

GTA is probably the most overrated game in existance. People only love it because it's advertised in every page of every magazine but in reality its not really that fun. Put enough of advertisement for something and people will buy it and like it just because of that.