Gears 2 had some pretty awesome moments, one of my favorite games this gen for sure. A few too many scripted moments, and the dire attempts at giving the poor dudes some humanity were bad, but the game kicked ass. Gears 3 will probably end up being the best action (adventure-shooter) game of the generation, unless ND manages to squeeze out another game before the end of the generation.
That's single player. I haven't played much of the MP. I liked the Invasion mode of UT, but I never got into Horde like I thought I would.