The plot is not about whale goo - That is one operation of many the humans have on pandora to generate revenue/grow their operation.
The humans have come to Pandora to make it their home. The villains and their goal is stated clearly and early on: eliminate Jake Sully.
This movie succeeds in setting up each of Jake's children, the reef clan, the humans motives and still presents questions to be answered in the next film. Mainly: How ill Kiri's connection to Eywa develop and will Quaritch choose his son Spider over the tyrannical human invaders.
Another gripe I keep seeing is the inclusion of the word "bro" into the script. Again it is clearly stated very early on in the film that these characters ARE NOT SPEAKING English when they speak to one another, only when interacting with humans. Think of it this way - the children are still saying the Na'Vi equivalent of "bro" because they are teenage siblings who use slang in their language.
The people writing these hater reviews are old wrinkly suits who REFUSE to have a little fun.
The movie is a blast. If you liked the first one you will love this. No one is claiming this sort of movie is for everyone. The people leaving negative reviews went into the movie knowing their answer and they did nothing but look for things throughout the film to try and desperately claim how bad it is.
Go see this movie! It's a good time.
It's not James Cameron's fault you guys can't pay attention to what the characters are clearly stating and setting up.