Need to post an Avatar review, but in sum: "magic honky" criticism is valid but overstated, the effects are paradigm shattering. Go see.
On reflection, that mostly speaks for itself. I don't feel a need to amplify those points much if at all, except to say, go see the damned movie on the big screen. In 3D if possible. If you're any kind of cinemaphile or media fan, you'll regret it in years to come if you don't.
A few other (mostly non-spoileriffic) comments...
James Cameron got the grammar and form of 3D right. This is the first time I've ever seen a movie in 3D that didn't feel like a stunt. Some scenes in this movie triggered severe vertigo in me, the sense of depth was realistic. (That's a plus, by the way, in case you were wondering.) That alone makes Avatar worth seeing, if you find filmmaking trends interesting.
The renderings were incredible. I think Cameron has bridged the Uncanny Valley with his Na'vi, but it runs much deeper and more detailed than that. The gums of the jaws of the forest animals, for example. I could watch this movie half a dozen times just to track the different sets of details.
Yes, the plot is stock, bordering on fatuous, with a shot of magic honkydom. But it's serviceable, and given all the other things this movie is trying to do, a serviceable plot was probably a better choice than something subtle and sophisticated. I say this as someone who is normally very focused on screenwriting and plotting as part of the movie experience.
By the same token, I could spend some time whining about world building and SFnal gaffes of various sorts. I may in fact make a future post about what bothered me. But as with the plot, that's not the point of this movie, and I'm willing to accept some stock SFnal cliches in service of such an immensely immersive and captivating movie experience. Like the plot, the SF worldbuilding could have been handled (much) better, but the SFnal elements did what they needed to do.
However, I'm betting the same stock approach to many of the moviemaking elements will keep Avatar from being another Star Wars. The two films have a lot in common, including the high likelihood that Avatar will be a seminal moment in a new era of moviemaking. But the sheer, raw fan appeal of Star Wars was drive both by the Campbellian appeal of the Akira Kurosawa story (cf The Hidden Fortress) and the broadly accessible archetypes of the ensemble cast. Between Luke, Leia, Han, Obi-Wan, even Chewie and the droids, there was someone in Star Wars for almost everyone to identify strongly with. Avatar is more emotionally remote in that sense, and I don't think it will generate the same level of fan loyalty. I do, however, predict a strong future in Na'vi fetishism and all that entails on the seamy underbelly of the Internet.
All in all, even with the obvious and not-so-obvious flaws, if cinema is an important part of your entertainment life and cultural experience, go see Avatar in the theatre. Several times, if possible. It really does bear up under the weight of expectations.