A large part of the appeal in Gearbox Software's Borderlands is the multiplayer, which allows up to four players to join together in the campaign. Most of the game is actually pretty bland and repetitive, but the multiplayer makes it feel rewarding. Well, leveling-up and collecting loot is pretty rewarding in and of itself, but the multiplayer really seals the deal. There aren't a whole lot of games out there that allow for this style of multiplayer, dropping-in and dropping-out while working on the full campaign, upping the challenge and rewards with more players. Which is a shame because it's really fun.
I don't have much else to say besides that, but if you click the "read more" stuff you can watch an amusing trailer about how awesome Borderlands is and why it's not for mainstream sissies. Oh, and a sound file of some excellent in-game music.