Replay value, that's it.

Usually If i play a game again it's good, if I play it over and over it's excellent. else why would i play it so much?

When I'm playing a game and I think to myself "Wow, this is fun".

Let's not make this complicated......what makes an excellent game is the FUN FACTOR

Fun factor, but also games that just make you go wow! like Uncharted

Not every game can be judged by the same criteria. However, I'd say that a great game is largely defined by gameplay that is fun, original, well polished and has good controls. Having an appropriate length, good replay value, music, sound effects, voice acting, visual presentation, art direction and solid frame rate also helps.

Well I think that great games can get over many of those things, like Mass Effect is a great game without a solid frame rate, and Uncharted is a great game without an appropriate length, it was also not that original, but it was still great

actually, on an added note, a good soundtrack can greatly increase my opinion of a game (I wouldn't like the MGS or FF series nearly as much if it weren't for the soundtrack)

@Munkeh111

I have to agree because no game, no matter how great, is flawless. All great games have to overcome their shortcomings.

A game must have good controls, if the character or parts of the game do not handle the way i want them too then the game has failed. And any game that uses motion controls for more then two seconds has also failed.

For me its just Fun, and also I have a pretty short attention span and pretty busy schedule so games that can be played in short bursts that you can leave and just pick up and go.