What makes for a good game?

Looking at games of all years, from Pong to Crysis, what makes a game good? What single factor is it that makes us gamers sit in front of the screen, and oogle for hours at a time?

Plot or Online gameplay.

Bioshock demo. Amazing narrative, crisp graphics and distinct style. As I played, I grew more interested. The characters, Atlas, Andrew Ryan and Big Daddy are all fresh and interesting. The plot is what drove me in. I bought it.

Call of Duty 4. Singleplayer... shorter than usual, but definitely engaging. Awesome team-based action. Then on Live, we have multiplayer with tons of modes. There's perks and an unlock system that makes playing it rewarding, as if it wasn't great enough. Definitely online gameplay here.

But I think the third factor is yourself. I mean if I could say CoD4 is about spawning, running around and shooting people, which it is, which all FPS are. I like the game however, and that makes it great to me.

According to Sid Meier, "...a series of interesting choices."

That doesn't really apply to games like Guitar Hero I guess though...