I prefer to find a game that is 3.X series. My buddies and I have a saying, "Just say NO to 4.0!"
I enjoy any campaign setting, whatever theme. I'm pretty easy to please. The one thing I would really hope for, is to not limit PrCs, feats, and things of that nature to only one setting. Like, "We're in Eberron, and although that PrC from Forgotten Realms would be cool to have, sorry, it doesn't exist here." I prefer DMs and players alike to be able to take information from any source and apply it to their game. This allows for a much richer gaming environment.
As for the game itself, I'm pretty much a 50% RP / 50% Combat type of person. Don't get me wrong, I can go either way should the group be fun!
Blech. Been playing D&D for about 14 years (DMing off and on as well during that tenure), playing from 1st ed. to up to 4.0. Currently, I refuse to play 4.0 games. Nothing against the people that play them, just against WotC for publishing that material.