different trailer- be warned this trailer is long and practically reveals the whole storyline.
http://www.youtube.com/watch?v=y35kq3H0ISc&feature=player_embedded
I think the detail of the CGI is amazing but I honestly cant say it looks realistic to me, its not just the design, some of the navi/avs movements are very stiff and the navi & other creatures look so glossy. I think the environments looks more realistic.
That is a fan-made trailer... Cobbled together from the two official trailers and the "vision" featurette. A nice editing job nonetheless.
Regarding the CG realism thing... Sure there are a couple of scenes in the trailers that look a bit iffy. Then there are scenes where they just *nail* it, like this picture:
http://thefilmstage.com/wp-content/uploads/2009/10/Avatar61.png
Some may quibble about the design, but dammit that looks *real* to me. If I didn't know the Navi were CG, I would assume that is some pretty amazing makeup.
Hopefully they have some time to tweak the remaining scenes to a similar level. But even if they don't... It hasn't stopped me from enjoying movies up to this point, so why should it now?
BTW, this is just a cool image:

http://thefilmstage.com/wp-content/uploads/2009/10/Avatar102.png (note the bayonet on the Mech gun)