I went to WDW this summer, not really having watched Avatar (DD watched it once and I fell asleep lol). I did FoP, NRJ, ate at Satuli Canteen, and enjoyed looking at Pandora. But, NRJ made no sense to me and the whole area just seemed odd until nighttime, then it was gorgeous. DD15 and I went back in October and I made it a point to watch Avatar again before we left. I am so glad I did! NRJ was meaningful and beautiful this time around. I was unable to do FoP (major motion sickness first time and didn't want to risk ruining a short trip), but the entire land of Pandora made so much more sense after watching it. If you can find time to watch it, I recommend it.
The movie isn't terrible, but it isn't that great, either. The story behind it is like Ferngully, I will agree to that, but the language is not kid-friendly. So if you limit swearing around your child and in the movies they watch, I don't recommend watching this movie with your child. I was actually surprised at the foul language. Don't get me wrong, I swear, sometimes I swear a lot, but for something I'm considering now a Disney-esque movie, there's a lot of cussing. The movie wasn't good enough IMHO to make multiple sequels and an entire land at AK, but maybe the sequels will be better.