So, what makes a game great (worthy of high scores)?

[nintendo_fanboy]

It really should be about nothing else than having fun while playing it. You must want to play it all the time.

At least that's it for me. I have noticed that with the games that are really on top in my books (Mario platformers, Zeldas, Tales of Symphonia and the Golden Suns, and Okami is shaping up to be one too) I play them also at times I usually don't play games because the time frame is quite short or something into that direction.

You should never get annoyed by the game either. Often, even in great games, there are parts when you have to get over yourself to play it because you know that it's just not fun. Grinding parts in RPG's for example.

If a game really fits those two descriptions, it should get scores no less than 9's. Often there are other, irrelevant factors included though.
Lenght is the worst in my books, because it is so much better to have a short game that has no letdowns instead of a longer one that has.
Difficulty is another one. As long as the other two things are given, why should you care about difficulty? I know that it can be very satisfying battling a boss time and time again until you finally beat him, but it can also be annoying if the fight isn't fun.
Graphics are obvious. If the graphics are so bad that they affect fun, then they are already included in that factor. If they aren't, why should we care?
Story also belongs here, although this can be an argument in story-driven games, because it can be fun playing a game although it has a bad story, but a good story can really give a game the edge without affecting fun. This should only make a game get scores even higher in the 9's though.