I took Borderlands back in order to get Bioshock for Andrew to beat (He loved the second one btw) He's going to post reviews for both of them in a bit. When i took it back and Borderlands was rented out, I rented BF Bad Company 2 and I think I'm almost done with the single player. If you enjoyed the first game and it's story then you'll enjoy the second one. It seems that EA improved the game in almost every way possible.
The story isn't quite as good as the story in the first game but it's very good. Gunplay and weaponry are very good and this has to be one of the best looking games I've ever seen.
Bottom line is give it a rental if you liked the first one. I plan on diving into the mp once I finish up the single player.