I m wondering the same :
is it possible for R2 to get better review than GoW2 :
goW2
better gfx
10 hour campaign
solid online play
not much improvement from GoW1
R2
worse gfx
10 hour campaign
very very solid online play
lot of improvement
I can see some reviewer rating R2 higher because gfx are not everything.
But I m not sure that R2 will get a better average review than GoW2.
Wait and see.
Time to Work !