I haven't seen the flick in question, but the more you read and watch movies in your lifetime the more marginalized the movies you like are.
This is what a lot of movie and book critics love stuff the general population finds very un-entertaining. Case in point check out a movie called Goodbye Solo. It is a interesting story you probably have not heard, with interesting direction and good acting, critics loved it, but try finding 20 people in Ohio (or Florida etc) who find it interesting. Heck I liked it but no way would I A) pay $15 bucks to see it in IMAX or B) watch it again. There are a lot of movies that fall into this category. No Country For Old Men is one, that I still love, but I don't need to be kicked in the nuts by a movie so I really don't want to watch 3 times in the theater.
From all accounts Avatar isn't a original story, but is entertaining a bunch of people so Hollywood loves it. Plus if it has great appeal to children you can bet you will grab at least one parent so that ups your ticket sales.