I've only posted once previously about a movie I've seen (that being this post about "The Curious Case of Benjamin Button"), but "Avatar" was compelling enough to me to warrant mention.
What was so interesting to me was both the story and the technology... both of which brought to mind other great films.
From a story perspective, the same "epic tale of life" that I liked so much in "Titanic" (of course also directed by James Cameron) and the aforementioned "Benjamin Button" were both here, but really... "Dances with Wolves" is the movie I most thought of based on the plot.
On story alone I would have found it a solid movie, but what really took into into a higher category for me was the technology (and I highly recommend watching it in 3D). It was amazing on the screen... and also fascinating to view the movie in the context of it being likely the first in a long line of current 3D technology live-action films.
Based on this front of the curve usage of technology and coupled with the great story, the comparison film that probably most comes to mind for me is "Star Wars."
Quite a comparison, but "Avatar" to me was quite the movie.
Postscript: Ok, after thinking about it further and being a few days removed from the amazing 3D effects, I feel now the story probably wasn't the greatest in the world (and certainly not up to "Star Wars" story territory), but the technology made this a great film to me.
To that point... interesting BusinessWeek cover story on James Cameron a few weeks ago.
Titled "King of the World (Again)" the piece details how even after the huge success of Titanic, the director had to win over sceptical studio executives when he expressed desire to make the most expensive movie ever filmed. In fact, he had to put his own money in to help develop the cameras used during shooting... which should pay off nicely for him with other directors interested in that technology for their own 3D films.