The point was to satirize your assertion that there are no objective standards by which to judge a film. It was backhanded because I knew you yourself didn't believe this, or you wouldn't keep making grandiose claims to universality. You want it both ways; my private subjective opinion has universal objective validity.
So now in a roundabout way, you've unearthed the hidden rules by which you've designated AVATAR as a great film.
They are basically: Because avatar is art and art am good.
See, a work of art has aesthetic qualities, and it has underlying concepts, and its meant to stimulate the viewer.
AVATAR does these things. So AVATAR is art. And art is good! AVATAR is good!
But after we've established that AVATAR is art, isn't there another step to take? a way to understand whether its good art? I mean, technically, every fucking film ever fits the criteria you've set down. Good Burger!
The Stand is literature! you might say. But is it good literature?
So lets say that filmmaking is a type of art, and it has its own language of expression, and if it can use that language in a sophisticated way, then its good art. AVATAR's language is extremely simple and derivative. So fine, it's art. So what?