Most people here talk about the visuals, but Avatar was much more than that. While I admit that the 3D visuals were absolutely amazing, the messages conveyed in it were beautiful.
Respect nature, accept the hard parts of life, trust in oneself, understand ones place in the grand scheme of life, compassion. The movie also showcases some of the problems our current society is invested in.
Great visuals, likable characters, creative aspects, inspirational messages. Highly recommended.