I played Borderlands a bit with some friends, but it got old pretty fast for me. It's basically a ghetto shooter MMO, lotsa quest grinding, not many 'raid' bosses, or much endgame content. When I hit 50, I just farmed a ton of purple/orange items and I was done. That was back when it first came out, though... Maybe there's more content now, but I'm not going back.
I'm addicted to Bioware games

Mass Effect 2 is sooo much better than the 1st one.... There's always something do, the story is rich (I didn't care for the somewhat shallow storyline in the 1st one), better gameplay, and more party members with interesting romance options. I liked it enough to play through it again. They didn't get rid of the waxy skin look for the females, unfortunately lol
Dragon Age is a good game, too :] I'm waiting for the expansion to come out.
Honestly, I think I've played them all.... at least, the ones available on Steam :/ And I've become very picky. I haven't found a good multiplayer game to settle on. L4D, TF2, they're fun, but I've been playing those a long time and now I'm looking for something new.
Anyway, if any of you play on Steam, send me a private msg with your Steam addy if you want. Maybe we'll get into the same game sometime.