I saw the movie in 3D on Sunday with my son and we both enjoyed it! The story was decent, if predictable -- but most stories these days have a basis on or elements of some past story or event, so there is nearly always some predictabilty. Does not bother me.
The CGI was awesome. Could they have done things differently to make it better? Sure, but I don't believe that there is any movie to date that comes close to the quality of CGI in Avatar. The 3D was also good -- again it could have been done better, but I did enjoy it.
If you enjoy a well done movie, then you should go see Avatar.
One more comment, or explanation, really. I enjoy most movies that are meant to entertain (not all, but most) because I set my expectations appropriately and don't over think them. I am there to escape, to be entertained, so I go to the movies (or read fiction) in a way that I am likely to get the most escape / entertainment value out of them.
On the otherhand, I enjoy a good documentary (e.g.,
King Corn -- which I highly recommend) and watch these kinds of movies with expectations that are different because they are not meant to be entertainment.
It's all a matter of how you approach things-- is the glass half empty of half full? (and full of what?? a good single malt scotch or tequila, I hope

)
Time for a good cigar!