Fantastic!
The multilayer mode really isn't my kind of thing so I didn't play it very much.
The story is alright, not too creative - Muscular rough space age men wielding big guns shooting hostile aliens while trying a way to destroy the alien infestation on earth...Nevertheless, the ending cinematic made me wish that GoW 2 was already out, I want to know more about the aliens now that they seem less..."typical"
The only level that really bothered me is the mine cart level. This level was annoying and really not any fun, and on the hardest difficulty it took a long time to beat (especially on co-op because neither of you can die/make a mistake)
The reload mechanic may be silly, but even after doing it a couple of hundred times, I still get a sense of accomplishment when I get it timed just right.