Variability.
Like, not being too repetitive, and also the ability to do things different each time. Both on a large scale (choices in a game e.g. ME2) but also small (in the gameplay e.g. realistic physics and intelligent ragdoll effect (euphoria), or just various ways of doing stuff).
Also replayability on a large scale, like restarting with different classes or paths.
For me, spectacular graphics, animation, physics and sound often satisfies me.