Players who are on their toes, use their heads, role-play and not roll-play, and know how to develop a character instead of read a character sheet.
Long time gamer. While I am primarily interested in D&D (pathfinder or updated 3.5e) right now, I occasionally have played and run other games, such as D&D 4e, Call of Cthulu, Vampire the Masquerade, Paranoia and a few others as well as board games-o'-plenty. While I mostly enjoy running a game, I do enjoy handing over the reins or joining as a player from time to time. Usually the games I run are with more mature players (ages mid 20 - 40), but all and any age are always welcome. Most games involve roleplaying, an open mind, and mature themes/language (not for the meek or timid). My games usually have deeply involved plots and expect to be using your head as more than a hat rack - though a good epic hack and slash battle from time to time is ok too.