Fantasy/science fiction films often have trouble convincingly transporting their audience to unfamiliar worlds but Avatar knocked that out of the park.
However, the storyline was uneven, dragged a bit and the characters were all little more than stereotypes. Plot developments were fairly predictable and the morals of the story were repeatedly shoved down the audiences' collective throat. I didn't go to the movie because I expected a brilliant social commentary or an intriguing plot. I went because I wanted to see them blue alien dudes shoot stuff and fly around on big ol' lizards. I left contented.