The loss of WOW factor is true. When the first Gears came out it was the definition of next gen graphics and I'm sure a lot of sales could be attributed to that.
Gears 2 won't have that luxury, also it has 2 key multiplayer 360 games to contend with: Halo 3 and COD 4 which have huge loyal fanbases, that already decreases Gears 2 sales.
I still think it will sell very well, maybe it will outsell Gears 1 (install base+hyped sequel) but will it outsell Halo 3 or COD 4? not likely I think.

Thanks to Blacksaber for the sig!







