This has to be one of the best sequels I've ever played. If you loved the first borderlands then you definitely should rent/buy this one. Besides a a few problems (quests,guns will sometimes go underground) The game has one of the best co-op I've seen in a long time.
-Great art design
-Enough stuff to keep you busy
-Co-op (both online and split screen)
-Zillions of gun variety(color,stats,effects ect.)
-People can take your drops and leave (kinda sucks but ohwell)
-Some quest related guns will drop underground (Dr.mercy for example)
If you don't have friends to play this with online it's not worth playing. Alone the game is tough and a bit boring. With random people it's infuriating since the game structure isn't designed for such play even though it's offered. Between loot hogs who take everything, not being able to travel between areas unless everyone is ready and out of a menu, to the abundance of quests where everyone wants to do a different one at the same time, the game is a mess unless there are civil people. And with random people that doesn't exist.