Having played quite a bit of Borderlands (beat the game after 36 hours this weekend), I can say you'll probably enjoy it.
:)
My personal take on the games mentioned.
Fallout 3 is like wine. It's a game I tend to savor, take my time with, let it "breathe" and appreciate over the course of it's own history.
where as
Borderlands is like going to that rowdy sports bar and doing shots with the crew and forgetting my own name.
both games are fun but in different ways. One takes patience and dicipline, the other takes a designated driver and a good hangover remedy.
Fallout, for me, requires some note taking as to remember where my char left off, so coming back to it from my other "two night kills" becomes alot easier. Very easy to play several games and still play F3 while the other games hit the shelves. I tend to do this with deep games, while also playing the lighter ones at the same time.
d