A fun game to spend a few hours in. But don't fool yourself with unrealistic expectations.
I know there is a lot of expectations, but don't fool yourself talking about 12 years in the making. The game was dead until gearbox picked it up 1 or 2 years ago so you probably should think of it as you do for that direct-to-video movie rental you got just for spending a good time in the Sunday afternoon. It kinda sucks because its just straight, and not cutting-edge, but you like it anyway, and that is what is important.
If you can, buy it, but if you can't just rent it, it is not an instant classic but i can guarantee you will have lots of fun.