I'm a fairly serious player, and prefer game worlds that are fairly developed or thought out. Original homebrew worlds can be a plus. However I am perfectly fine with developing game worlds, and would be willing to help flesh them out. I generally prefer fantasy to sci fi.
While the two game systems I'm most familiar with are White Wolf (storyteller for vampires) and DnD (played seriously for a year), I am open to other systems. For white wolf I was a storyteller for VtM before I left. For DnD I have rped as a lv 14 shugenja, 2 clerics whose levels now escape me (they were above lv 6), and have rped as a floater pc lv 11 bard. I haven't played DnD for almost two years, but I keep myself updated and have the core 4.0 rulebooks.