To talk about this briefly, I have for a while; seen four things being potentially able to match Potter.
1.) Star Wars Land - Unlike Pandora, this to me from everything in the concepts and what has been said; does excite me more-so. I think it will be fascinating to see in the near future what they can do, and that I think this will be in a strange way, a Star Wars Fan's dream come true. Especially with it being canonical to the films, I do think that there is a lot of great potential for the land.
2.) Super Nintendo World - If I was going to say something more direct (rickroll), I will say this. This; is Universal's next big risk. Nintendo, is one of the largest IP's in the world, and that it can easily be botched and poorly received for not immersing yourself enough to the world. I think, that if they embrace that you have to experience it, not by a screen; but with real environments, it will be the big selling point. More-so than even the characters. It's the experiences and the atmosphere that they offer, that will drive this whole thing from being a true disaster, to a true dream come true.
I have talked with some collegues of mine, that I talk with on The Coaster Casters; that Nintendo is going to be a hit, if done in the right way. One simple mis-step can lead to a series of heartache.
3.) Lord of The Rings - This, to me; is Pandora's Box. Whoever would get it, if the Theme Park Rights can occur, to whoever in god's name it may be; must be careful with the IP. More so than Nintendo, more so than Star Wars, and more so than even freaking Potter. As one simple mistake, can to me; cause something more massive in the amount of backlash for an IP. Lord of The Rings, is legendary in pop culture, and it is one of the most defining stories of the medieval/fantasy genre.
There is a huge amount of backlash, if they even announce it; and that it would be an insane uphill climb in my eyes, that this would even make a freaking dent.
Universal, and their plans with the southern property
To put it simply, history has it's eyes on them.
The success of everything they have led themselves too. Everything, that they have done; has been with the aid more-or-less in the past few years; with Comcast. Now, what in the hell; would happen, with them doing the southern property. There are many way's that they can go wrong, and many ways that they can do something legendary. I think it is going to depend on how serious Comcast gets with this. Because it will be one of the largest investments to Orlando in years.
That being said, back to Pandora. I do believe it is beautiful. And, that I agree with many of the points from @Joe
, and @SeventyOne
; and that I hope to be wrong in my fears and worries. I do have hopes that they do something extraordinary with Avatar, but I have my doubts.