There's going to be some spoilers ahead, so consider yourself warned.
My praises:
-Visually this was amazing, though there were some scenes where the CGI seemed to be not as good as the first film. Could be I'm remembering the first film's CGI better than it was as it's been years
-All the water and underwater CGI was amazing though. Loved that
-A lot of the action was great, even better than the first film
-Neytiri (Jake's wife) is even more of a badass in this, liked that
My grievances:
-Story wise it was at its core a rehash of the first film, they just added water scenes to it. So that was a large gyp
-Quaritch was a good villain in the first film, but his blue-self and his blue-goons were kind of lazy replacements. Lends back to the plot being at the core the same as the first film
-The heavy teen-element was annoying at times
-Sigourney Weaver's daughter, aka "the chosen one" as it seems they're going with, was largely annoying
-Replacing the driving element of unobtainium with whale-brain-goop was lazy, they should have just stuck with the 'humans want to terraform Pandora because they've poisoned Earth and need a new home' angle' which they brushed on
Definitely needs to be watched at the theater at least once for the visuals, don't wait for the home screening.