You're right...It's better by all box office accounts. People saw that movie repeatedly.
With another 2 movies on deck, I'm betting that many more will learn about the Avatar universe. The world will continue to gain depth, which leads to more possiblities for the new expansion for years to come.
To me: The haters are already boiling into a few main arguments:
1)Want to keep all park rides Disney Specific (If Disney had done Avatar, would you still be complaining, or saying "it took long enough?")
2) Those that simply don't like the movie. I'll group the "Harry Potter is the best and nothing can compare" in this as well. This is a matter of personal preference.
However, it's insane to think that the highest grossing movie of all time is going to have its sequel fail. This franchise is going to grown and expand for a long time.
1) I don't care about it being Disney Specific, I care that it makes sense thematically, Avatar simply doesn't fit into Animal Kingdom, if they had announced it for EPCOT, I'd be fine if not excited for it.
2) It's not a personal preference (I hate both movies) it's a simple matter of fact that Harry Potter as a property is a billion times more popular and loved than Avatar could ever hope to be. You can see for yourself, find 5 people within the immediate vicinity that can name at least 3 main characters from Avatar, now do that with Harry Potter.
3) The success of the sequels depend entirely on how well loved the characters are to warrant a sequel to begin with. Avatar doesn't have that. People saw it because of all the 3d talk not the story or the characters. If anything reception to the sequels would be more like The Matrix sequels.