I haven't played it yet, but I've played a fair amount of the first one, which was pretty good. Got a bit repetitive, but it was not too dissimilar to Fallout 3 if you've played that.

From what I've read Borderlands 2 is a big improvement on the first, so for under a tenner it seemed like a good purchase.

That said with everything else I've bought in the sale, I don't know when I'll get around to actually playing it!