While Gears is pretty lame and uninteresting, I think you guys are reflexively exaggerating it's crappiness in reaction to Nemmies monumental wrongness about everything.
I don't really see how any of the Gears are really stereotype enforcing, aside from maybe Baird and the Cole Train. The only "stereotype" you could really attribute to Dom or Marcus are that they look like they're on roids and are tough. But if that was the case... all video game characters suck.
Imo, Gears suffers from the same problem as characters in the PT. They have actual personalities and some layers of depth, it's just shown in a really ineffective way. It's hard to realize that Marcus is actually affected by all the war and death around him when only 2% of his scenes involve a sorrowful expression or dialogue, while the other 98% consists of "**** yeah! Get back in your hole, *****!"