It really depends on the property and how rich a setting might possibly be for exploration and how much you can actually build from the source as far as IP-based lands go. Carsland was kind of a case of overdoing it, but Lasseter's weird obsession with the franchise actually ended up paying off and it's expansion of Radiator Springs compensates for the flaws of the source material and it ends up being a pretty good Route 66 land. The Beauty and the Beast section of New Fantasyland is incredibly successful at bringing in all the key locations of the movie to life. Universal's doing a great job bringing the settings of Harry Potter to life (though I don't like Dueling Dragons being a naked coaster) and Springfield's turning out pretty decent for the limitations they had.
Avatar is a movie that was more green-screen then anything else and it'll probably rely a lot on simulators more then anything else. And aside from riding with blue pterodactyls, none of the animals really stand out as creatures that'd be interesting to have an experience with seeing as they're just blue recolors of Earth animals with extra limbs. It just seems like a property that could really only support a standalone ride rather then a full land. You have a queue in the human base, then you go out exploring Pandora on a simulator and paint with all the shades of blue of the wind and that's really all you can do with it because we cannot build real flying mountains.