TLDR: No actual character development, rushed graphics, rushed scenes, motivations for some characters were terrible and many pointless moments.
** MAJOR SPOILERS AHEAD **
I want to preface this noting that I was a huge fan of the original Avatar movie. I came into this movie with excitement, but a fresh mindset as to not be biased with my affection for the first film.
Avatar The Way of Water was genuinely a terrible movie. I am baffled by how many 5 star reviews it received on Google.
Spider's character was terrible, as well as the actor of choice. The motivation of the character was completely pointless in this movie. Spider puts full trust in Quaritch, after a simple lie. But throughout the movie, Quaritch proves time and time again that he should not be trusted. As to why Spider trusted his just-met father over the people who raised him was completely pointless and actually proves detrimental to the the main characters. Now, I'm not bashing that part of the plot; but as to how the trust was formed was executed poorly; Again, Quaritch proved time and time again he was not to be trusted.
Kiri was also terribly done. She had absolutely no lore or any character development. Writers of the movie decided on making her "Weird" in the sense of typical awkward teenage girls. But then that weirdness develops into being able to control animals around her. There was absolutely no development as to how she understood these powers or even how she got them. I'm sure this will develop in future movies, but as of right now this was executed terribly.
Besides character development, there were many times in which the movie had pointless moments other than to extend the movie over three hours; One moment specifically when the youngest daughter Tuk gets captured multiple times when she could've just stayed locked to the railing.
Another moment being when Sully strikes down Quaritch and doesn't finish the job; Instead allows Quaritch to escape and reconvene with his team. Sully then disappears from the fight only to re-appear later when his son is shot. There is absolutely no development with what Sully was doing during that time.
Besides broken plot points and pointless character developments; There were scenes in which characters looked amazing. Other times, it looks like a cut scene from a PS3 game. As if VFX artists weren't given any time to perfect the movie like the original.