Plot - For me, the story makes the game. A decent story can make an unplayable game playable (ie. Lionheart)
Great Characters - If you're going to have a party, you have to have some characters that you like, someone with a personality that makes you think twice before using them as fodder for the enemies.
Villians - Should not just be your average 'Destory/Control the Universe' guys. They should be *really* evil . They must earn the title of 'Bad Guy'.
Music - Gotta have something good and epic to listen to.
Completely Over-The-Top Spell Effects - Rune of Torment, Mechanus Cannon, etc.
Dialogue Options - I like to choose what I want to say to someone, not let the game choose. This should also include different dialogue depending on race/class/skills/alignment.
Replayability - Randomly generated maps from Diablo don't count.
Point - There has to be a reason for playing the game; you have to feel like you're doing something important (and this is why I hate Morrowind - wait, no, I hated everything else about Morrowind as well).
Ending - The ending has to mean something. I don't want to have to spend the whole game boosting up my parties skills, and then have to fight the final boss alone, although this can work if done well (KOTOR 1, Torment). I also don't want to have spent 20+ hours on a game and then have a dodgy, unresolved ending.