I personally didn't mention Gears of War because I don't like it, but I know several people who did. What I can never figure out, is why Halo is such a system seller. It' just another generic first person shooter. Maybe it was revolutionary when the first and second games came out, but it's nothing special now.
Halo is much more than a generic shooter. Most FPS games only function as FPS games. But Halo can be so much more. Racing, minigames, infection, and the insane stuff that gets built in Forge make it one of the best games out there.