I have to admit that I haven't been able to play much non-D&D or WoD stuff, but this is not for lack of trying. I've actually got a small collection of interesting games (In Nomine, D20 Modern, GURPS Discworld, Ninja Burger, etc.) which have simply gone unplayed because I'm unable to scrape up anybody who'd be interested in playing, even if I GM'd.
At the moment, I'm being rather enamoured of Nobilis, which is probably the most complicated setting I've laid eyes on, though the system itself is deceptively simple -- in order to even make a character, you have to ask yourself questions like, "What is Wisdom (or whatever Platonic ideal my character has power over), and if I add or remove it to or from an object, what happens?" As an example of this, I'm planning on running a test game online, and so I gathered up a group of about nine potential players and then got them to make characters and backgrounds and so on. I've lost about three or four people to the inability to think abstractly enough to actually even play the game. Very disappointing, but I suppose not unexpected.