I think Gears 2 will come out ahead. It's still pacing well ahead of the first game.
I do think that Halo is more accessible than Gears of War, and that's coming from someone who is a fan of both series. Gears requires the utmost patience in single and multiplayer as in, if you try to play it like Halo, you will crash and burn quickly. The only way I can see the franchise significantly increasing is if Gears 3 comes out on the next console and is some mindblowing experience that makes it "the game to have" (and is hyped out the wazoo, a la Halo 3) on whatever they call that console. Also, I'd say that Halo 2's multiplayer probably attracted some of those additional sales that the first game did not see.
themanwithnoname's law: As an America's sales or NPD thread grows longer, the probabilty of the comment "America = World" [sarcasticly] being made approaches 1.
