It takes the experience of something like Diablo and makes it incredibly slow. Lots of running about, clicking frantically on things, and then picking up the loot when they pinata into clouds of gold, weapons, armour and stuff to plug into said weapons and armour. It's pretty, and solves me two main problems with Diablo 2 - you pick up gold by wandering through it, and the world is persistent (randomly generated, but wandering back into an area doesn't re-generate it from scratch).
If Borderlands 2 wasn't due out tomorrow I could see this sucking up a lot of our time. As it is, I can see it sucking up a lot of our time in about a month!
Original post on Dreamwidth - there are comments there.