Gears of War: It's too dreary, generic, and in many cases dumb. There is a difference between UV light and manufactured light, Cole Train is almost as offensive as Skid and Mudflap, the characters are ridiculously proportioned, some of the "military" strategy in the story is ridiculous, and the whole thing just seems like if someone took a Michael Bay movie and wiped their ass with the film.
Final Fantasy 7 & 8: I hate Seven for what it did to the whole series, genre, and media as a whole, I hate Eight because it's a massive piece of crap with barely any redeeming factors (the only one I can think of is The Spoony One's review of it).
Call of Duty 6: I hate it for a combination of why I hate Fantasy 7 & Gears, and I also hate it for people thinking it's the second coming of Super Mario Brothers.
I don't hate Halo, because there seems to have been genuine effort put into the game being accessible, fun, and challenging, and while Halo 3's story mode is not exactly stellar, it at least has a good sense of progression, scope, and entertainment value.