Slow refresh rate and lack of depth of field. Time will improve these features but the film suffered for their lack. There were scenes where the sensation of depth was the perspective emphasized but they left me wanting to dwell in them longer. The color spectrum too will improve with time and too much towards the dark. After a while the story replaced the novelty of 3D as what grabbed my attention. Not into science fiction or fantasy books. There must be a ton of them though that have flying lizards and a jungle dwelling civilization that gets attacked. The hybrid avatar idea surely has been done a hundred times too. I'll wait untill 3D can be projected onto my retinas to express amazement at the technology.
I wonder how the movie would do if here is no 3D effects. Regardless, James Cameron is a genius. This sets a new industry standard to movies.
I think 3D has accounted for a small percentage of total ticket sales. The 3D version was nice, but there's a lot of room for improvement. Some people have slight motion sickness, contrast suffers and colors aren't as bright. The nature of a rectangular screen takes away from the 3D effect, too. A huge oval-shaped screen with maybe a concave screen or a ramping effect at the top of the screen would add to the illusion and make for one helluva show.