Borderlands 2 is one of the best games of 2012 for me. But then again, I most likely won't be playing X-Com, AC3 or some other big hitters this year, so it may be a bit skewed. I do echo people's feelings that the guns feel more sparse, in the sense that there are fewer 'good' guns. I also feel like they could have done a bit more with the grenade mods as well as relics/class mod stuff. The whole game feels really solid though and I'm quite happy with how they handled the humor. Would have loved to see the current cast be developed more since we're in a similar situation for BL3 in terms of what we know about these guys.
EDIT: Also, I'm not sure how other people felt, but I really, really didn't like single player near the end and a bit through the middle. Played as a cata siren and man, bosses were a huge bummer + getting forced to give up after seeing a JET Loader fly away. *sigh* Co-op for me is most definitely the experience you want.