A reviewer I listened to said that it had decent themes, beautiful visuals, but a predictable storyline and often literally laughable conversations.

He said that it was a good family movie, one where the main characters struggled with moving to a new area and trying to fit in with the local populace, adapting to their values, and resolving conflicts from clashing perspectives, which was something the reviewer said he could relate to as a father. But that the bad guys were stereotypical greedy human capitalists, that the resource they were trying to obtain that time was even more ludicrous than in the first movie, and that the movie solidly cemented the fact that James Cameron has no talent whatsoever in writing dialogue.

So basically, he gave it a mixed review. Not fantastic, but not terrible either. The scores I've seen mentioned in this thread come as no surprise to me.