Don't take your kids or mother-in-law to this one, but it's got a lot of laughs. I saw it at a midnight showing with a good crowd, so maybe I'm giving it a better review than it deserves, but I had a lot of fun.
I highly recommend paying the extra cost to see Avatar in IMAX 3D. The experience is unparalled. There are no surprises in the story, so the special effects are the only reason to see this movie. It takes full advantage of IMAX and 3D.