Borderlands was one of my favorite games of all time because it was just FUN and was entertaining. It had its own atmosphere that was original. It blended RPG and FPS elements and I found it refreshing and well implemented. Borderlands 2 continues this trend with not tinkering too much with the formula, but adding more to just about everything. The story takes awhile to complete and one of the few games I believe that's worth a $60 price tag. Even if the DLC is half as good as the first game's, there is plenty more to be had for this game. There's more story, which will either resonate in different capacities with different people. I liked the mysteriousness of the first game. I gave it a 9 instead of a 10 because this game isn't radically different and therefore the addictive quality of wanting to beat the game multiple times is not there like it was in the first game.
As a side note: The opening song is nowhere near as good as the original.