An RPG that I'm very tempted to try is Burning Wheel, a fantasy game that gets rave reviews for encouraging characters to take an active role in driving the plot. I love that in a game, both as a player and as a GM. So it sounds like Burning Wheel would be a perfect fit for me.
However, BW is also fairly crunchy--it's got a lot of a detail. I don't think it's excessively complex, but there's a lot of interlocking parts. And from what I've heard, it's so well constructed that tinkering with the system can have massive effects. I'm not sure that such a system is for me. I'm especially not sure it's for me when you consider that if I got the game and introduced it to my friends, I'd have to explain it to them. And I hate explaining complicated rule systems to others. If everyone got a copy of the game and read it, then I'd be more willing to try it. But I doubt that'd happen.
However, BW still tempts me. I'd love to give it a try, but I don't know if it'd work for me.
P.S. Anyone interested in learning more about BW but don't want to buy the game, check out the Podgecast. It's an excellent RPG podcast in general, but they love BW, and talk about it a lot. There's even a series of campaign recaps from (so far) two different BW campaigns they've played. Well worth listening to. And I really want to play in a game with those guys.