GameInformer released a few details for the sequel Borderlands 2. Although the details are few there are some great signs that the new game will be an improvement over the first.
First of all co-op will remain four-player, and the enemy and NPC AI has been upgraded and improved. Bandits will have class structure that will control what weapons they have, making it easier to counter-them and find new weapons. There is a new element Eridium, which will also serve as currency and a tool for upgrading weapons and vehicles.
You will not get to play as the original Borderlands characters, they will be NPCs in the sequel. There is a new character though, the dwarf Salvador (pictured above). A Gunzerker, Salvador dual-wield any weapon. Borderlands 2 will also support all new weapons, each designed to fit their in-game manufacturers, and the story will feature dynamic missions.
SOURCE | GAMEINFORMER