You couldn't be more wrong. I've been to Universal once, Sea World twice, and Six Flags once. I have no real desire to return to any of them (except possibly Universal to see the impeccable storytelling of Harry Potter). I do appreciate the Disney legacy, I'm a fan of the parks and the studios, and I have been very critical when I thought Disney was making a negative choice.
This decision is a risk. Lots of people in this thread have pointed out that the second and third Avatar movies might not be successful, the public could lose interest by 2017, etc. The dissenters can't have it both ways - they can't complain that this might be unsuccessful, and then say Disney isn't taking enough risk. Again, I hate to say it, but Disney's core market isn't you. It isn't me either. We're hooked for life, and we'll be spending our money on Disney no matter what (whether it's at WDW, DL, etc). Disney wants more people to come. This will appeal to people currently outside of Disney's demographic. Families with teen guys, for example. Young adults. Sci-fi fans. The millions and millions of people who enjoyed this movie more than Winnie the Pooh. Even though the movie might be PG-13, I'm sure the land will be enjoyable to people of all ages (at least more enjoyable to young kids than Tower of Terror or Dinosaur). This will be an area that kids, teens, and adults can all enjoy - I'm sure of it. And that is Disney's legacy when it comes to the theme parks. Disney's not trying to build what you want. It's trying to satisfy a very general audience, so whoever happens to come to WDW can enjoy it together.