Likable characters and a good story.
For the combat mechanic, I really open-minded: Fallout 1-2 style is great, I don't have anything against Fallout 3/TES style (more action oriented), old-FF style was "fun but fastidious", Baldur's Gat/Neverwinter Night/Dragon Age:Origin style is a little less "turn by turn" then Fallout 1-2 and, finally, the Dragon Age 2 (yeah, I piled them together) style is quick, strategic but can become a little bit to MMO style (you always spam the same spells/ability in the same order...).
So yeah, I love RPG
