I must say that Borderlands 2 has taken a huge jump, mainly in creativity, from the first.
The landscapes have a lot more depth to them, as now they have layers rather than just being essentially one big flat area with walls and a few jumps. You actually have to navigate the maps now.
The humor and references department was really set free on this one. I’m only a level 13 and just done Ellie’s first mission, I’ve already seen references to Fallout 3, Kenny Loggins, Presidents of the United States of America, and various other VERY random things. The gun names are a lot better in this one as well.
The difficulty has greatly increased as well, especially with enemies’ health replenishing upon player respawn. I’ve found myself actually being challenged and worrying about dying, and not just because I didn’t want to have to retrace my steps.
All in all, I would say Borderlands 2 (so far) has taken one of the biggest jumps I’ve ever seen a video game sequel make (without changing studios, platforms, etc.)!