In comparison to gears, pretty much everything will bomb. Does that mean every game coming out around the time of GeoW2 is a bomb?!
It is the life time sales that will indicate how well the game has done. With GeoW2, it will probably have most 360 owners go buy a copy close to its release (having had a big following since its original release and a sequal being anticipated since then) whilst the ps3 users will probably slowly generate decent sales over the next few months (had a smaller following since the original due to number of ps3 owners on release).