If you watch his early reviews, specifically Orange Box and Bioshock, he notes that it doesn't seem to be funny when he actually tells people he enjoys a game, so he won't be doing that in the future. He ripped the guts out of GTA4 and Just Cause 2, and went on to play both games for quite a while after the review. I think he downplays the things he enjoys about games, because it is less funny when he's being nice. He'll tend to skim over the good points of a game because every other reviewer has already done that.
In short, He's honest, but he focuses on the negative because that's what makes his cynicism funny.
In short, He's honest, but he focuses on the negative because that's what makes his cynicism funny.