My favorite setting besides Shadowrun is the world of Kult. Sadly, the rulesystem it uses sucks so badly, noone wants to play it. So I am now in the process of converting the Shadowrun rules to fit the Kult setting...
HAH!
I've been playing in the occasional Kult campaign for yeeeeeears now! First Ed, with the terrible skills and awesome wounds...the system is just about totally secondary to the gameplay for us, though. Stuff is winged (wung) to fit, and it doesn't really matter, since horrible things always happen to us in these campaigns. Horrible things that we SOMEtimes don't even bring upon ourselves!
Fave systems at this time (other than SR4a):
Pathfinder. Like like like. And it's not 4E.
SW Saga Ed. Despite that the vehicle stuff was dumbed down a bit, I liked it overall. We didn't have a lot of Force-using munchkinism, however.
Gamma World. More for setting than system. Hell, I even bought that HC set of the d20 green books when I discovered them. Not sure what I think about this upcoming edition, however. I actually agree that the 4E ruleset is not bad for the mutations, I don't like the CCG aspect as hinted.
GURPS. Played some coolio Supers games, and I even did up a GURPS Kult scenario for a local con one year. Very satisfying.
(That's all I got for 60sec thought...gotta go.)