Lots of back and forth on this, definitely interesting. I did have a thought that I didn't see raised elsewhere, though, on why this is a really odd move, thought I'd share and see if anyone had any feedback.
Avatar was an absolutely eye-popping movie, and it's not too difficult to imagine it being translated into a theme park, but as others have pointed out, it was the visuals, not the story, that drove people to the theaters. Part of the reason, I think, is that Avatar was the first 3D movie that actually offered the sort of immersive 3d experience that you got at -- wait for it -- places like Disneyworld. For eons, "good" 3D was only available at theme parks (with Disney leading the way IMO) and if you went to a 3D movie elsewhere, it meant you were going to see a movie that incorporated some choppy 3D effects from time to time.
With that in mind, there is certainly some irony in Disney welcoming with open arms a franchise that ushered in an era where great, immersive 3D could be found at any major movie theater anywhere in the country. I really wonder how some of Disney's 3D shows will stand up now that you can get quality 3D so easily -- sure, they have other interactive elements, too, but the "wow" factor of the 3D itself is going to slide away as more and more "regular" movies are made in 3D using technology that matches or exceeds what Disney has been using for years. If you can't beat 'em, join 'em, I guess?
Now for a less original, but still related, thought: I'm concerned that Disney is basically all-in on this with no guarantee that the 2nd and 3rd movies are going to be good enough to create the sort of franchise that you can build a whole theme park land around. Avatar was visually groundbreaking, but by the time 2 and 3 come around, it will be commonplace to see great visuals like that. If they don't similarly push the envelope from a technological standpoint -- and there's little incentive for Cameron to do so, frankly, because he's going to make a mint either way -- then it has to rely upon story, and that's somewhere that Avatar kinda fell short. Not that the story was bad, it just wasn't particularly original, and it was fairly predictable.
I'm definitely rooting for Disney here, and it looks like they intend to sink enough money into it to do it the right way. Moreover, Avatar does lend itself to some pretty awesome ride experiences and could provide a vehicle for Disney to do something along the lines of what Universal did with HPatFJ, which is the single most impressive thrill ride I've ever been on. With those things in mind, I'm excited about this. It does still seem odd, though.