The blue people are WAY taller than humans.
I think you can find a million reviews out there that will all tell you the same things about how this movie is so great and the story and setting and blah blah blah blah.
So I'll try and share some things that won't get written about as much:
1. The CGI character modeling was... better. I don't know how else to say it. If you take any other movie that had a purely CGI main character and hold it up to this one, Avatar will be better. I can't even rightly explain it to you... but... you know how when you're watching a movie and the CGI characters just never look quite right? This movie found a way, through just little added animations and small touches, to be better. In my head, I'll remember this movie as the first time I felt like the CGI characters stopped looking "not quite right".
2. The 3D was pretty cool. I'd never seen a 3D movie before, but two people I went with said that this was MUCH better than the last one they'd seen. I'm not gonna start seeing every movie in 3D because of this, but if you're genuinely curious about 3D, it sounds like this is the movie to test the waters with. It wasn't perfect, but it was fun at times. Oddly enough, the most impressive 3D effects came from some of the tamest scenes. Action sequences didn't really pop as much for me, but the shots of people just walking through the forest looked really cool, sometimes.
3. In almost any artistic medium, I'm always a big fan of a project where it is evident that the creator "left it all on the field" so to speak. If I really feel like you gave it your BEST, even though I may not like your finished product, I can at least respect it. I think that applies here.
If the stories about James Cameron wanting to make this for 16 years and spending $500 million dollars on production and advertising are true, then it's easy to see what makes this movie so good. It's not a fair world, and not every movie maker gets unlimited time and unlimited money to make their movie, but if James Cameron truly did in this case, then I really respect him for not wasting the opportunity. It felt like this movie was the work of a man who had an idea he really believed in and he wanted to see it through the right way.
This movie was AMBITIOUS and Cameron refused to make a movie that wasn't his best effort. I respect that, and I think he made a great movie.