Minor side note: while other people saw the movie multiple times, and I remember friends saying it was a mindblowing, amazing experience, I actually didn't see the movie until probably about 2013 or so. As I noted, I saw it at home, on my nice 54" plasma (which in 2012 was state of the art). I wore the 3D glasses for it.
Prior to that, I hadn't wanted to see it unless I could do a decent 3D watch of it, given that that was the big draw.
The 3D was initially impressive, but grew less so over the course of the film. Visually, it was pretty, but by 2013 when I was watching it, it just reminded me of a video game. Like, it wasn't that big a deal to me.
The thing that got me, though, was my general sense of "I don't get it. Why was everyone so over the moon for this movie? It's really nothing special outside of the visuals." And my ultimate conclusion was....that really was all there was to it. It was visually spectacular in 2009 and....that's it.
It reminds me of the hype that surrounded Final Fantasy: The Spirits Within when that film first came out. Another technological marvel in its day which has since been largely ignored. I watched that one, too, and found it about as "meh" as Avatar. The story was nothing special, the visuals were fairly impressive, and several years later, technology marched on in leaps and bounds and completely eclipsed what the film did.