[SIZE=1]Well, most of my bases have been covered by now.
The playability/time factor is a big one for me. I have long been complaining about the games getting shorter and shorter, not to mention losing any substance they might have had.
As Red mentioned, the story's a big part of it; if I don't have a storyline to go with, a lot of games are just unworthy of playing. Given, I play fighting games and the like, but even with those, I like to have a good story mode with a story to go with each character.
That leads me into my BIGGEST requirement for a game; characters. As a guy who has considered both psychology and creative writing as majors for college, I'm a sucker for well-thought-out or just plain cool characters. It's always fun to delve into a character's psyche and watch things play out in the game according to their choices.
Music is in there, too, but it's not so much a requirement as a bonus. Bad music can ruin a game, but I don't require masterpieces.
Interface is just like music. A bad interface or clunky controls can slay a beautiful or intriguing game's gameplay, while smooth controls on a game that could be hard to put controls on (A la the Armored Core series) can make games great.
Hope that all made sense![/SIZE]