Will anything sell as well on the 360 this year as Gears of War 2? The first game has sold over 4.5 million copies worldwide - a quite stupendous achievement for a brand new IP. Expect the second game to surpass that by quite some margin. We might not see Halo 3 numbers, but it will push it close, that's for sure.
If we look down the list at 2008's exclusive 360 games, there's nothing that can compete with this.