I didn't hate it but didn't like it much either, here's why......

Rating: 3/10 (19 January 2019)

I went in with zero expectations, also to let you know where I am coming from I saw this just today (2019) on BluRay, so not exactly what I'm sure is the intended "big screen" way to see this, and not ideal sound either.
That said, from word of mouth and reviews I knew that the visuals and stunning CGI were the main selling point of this movie but technology moves so fast that I think my expectations were too high on this point and the effects here have already been surpassed. I've seen better recently, including in the Star Wars movies (for better or worse), so the effects in Avatar I found good (particularly the more background stuff, like the "world" the characters walked through), but not STUNNING. This is mostly true of the characters which I didn't think looked awesome at all.
As for the acting, I have no problems with it. Worthington wasn't awesome but certainly was good. I like Weaver in whatever work she does. The supporting cast were all good. And Stephen Lang stole every scene he was in. It's great to see actually because I see him pop up now and then but until now I've never seen him in a really big, successful blockbuster. He may seem like an overnight success to many but he's been around forever (as a kid I remember him doing a great job in a show called Crime Story along with a similarly gifted and surprisingly versatile actor named Ted Levine) doing all kinds of roles and always doing a good job with it.
So visuals were passable (obviously they were stunning at the time and are still impressive a decade later which is good). And the acting was good. Which brings us to the real failing here, the story.
As other reviewers have said this story is very, very unoriginal. Seen-it-before plot points and tropes are piled on top of each other and nothing comes as a surprise. It's slapdash thrown together pieces of Ferngully, etc, etc... natives and nature vs. progress and development. "Oh my gosh we are the bad guys!"
And it is ponderously overlong given the basic story, and how predictable it all is. I don't think this story surprised us once even in 3 hours (oh also the version I watched was the extended collector's edition - maybe that is not as good as the theatrical?)...
Actually it is a testament to the quality of the visuals, the cinematography, the actors (working in CGI world), and James Cameron's direction that this overlong heard-it-all-before story never actually gets unbearably boring. It wasn't good but was never boring.
I would give the sequels a chance, and will definitely be seeing the next one in the theater. Still the story will need to be much more original, much better, and frankly to be considered an all time great I think a movie should have more staying power than just a few years. It already feels old to me, and it isn't sticking with me (I'm not thinking about it at all really) the way I feel "good movies" do.
Just my two cents.