Loved it. If you're looking for fun, it's the funnest. If you're looking for depth of character, unique plot, original story line, then no, of course not. That's not what Avatar is.
Based on my viewing I'd say Avatar is a viscerally brilliant, endlessly creative, technical showcase meant to amuse the masses. It's not Memento. I found it a brilliant 3D amusement park ride. I saw it in IMAX 3D Digital as well as RealD 3D.
Is it a "good movie"? In context of what it is it's the best to date. But if you're looking for a movie that meets all criteria of a truly "great film" (e.g. Citizen Kane, Pianist, Gone with the Wind, Raiders) of course not. Not even close. Two completely different types of movie experience.