A few points to make having been to DAK today. Pandora needs to be incredible as I spent 2 days of this vacation here:
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We were so taken by the Harry Potter lands, and the promise of a fantastic water park to come - that my wife and I bought UNI annual passes!! And I must say that Gringotts was EXCEPTIONAL!! We went on it several times. I am not a big thrill ride person, but this ride provided mild thrills but with so much more. It was a unique experience that my wife and I loved.
I am now a UNI fan for their new attractions. To be completely transparent though, I found most of USF to be not that great. We enjoyed IOA much more. That being said, WDW is still head and shoulders better to me (for many reasons). But they need something new, and they need it to be big. When I look at Pandora I believe it will be. I don't think that it can compete with Potter's popularity, but I think that the theming and rides can. Time will tell. Believe me though, when you see Pandora growing in front of your eyes, it is hard to believe.