The big thing about this movie isn't it's plot, or acting, or setting; Its the way they filmed it. Jackson's new Virtual Camera is being tested in this movie, as well as new ways of transferring live actor's motion and expression to their digital counterparts, and improving the 3D movie experience.
The idea is that most '3D' movies are basically the same as the normal version with a few moments where something sticks out of the screen at you. Avatar is supposedly all 3D, all the time, which is why CG is used to such a heavy degree in the first place.
The trailer portrays the crippled soldiers being transferred into the alien bodies. The alien form is the same actor as the human, using motion capture to fit expressions and movement to the virtual body.
While it'll be interesting to see how these new technologies work out, I have to say that the movie itself looks a little bland and trite. I can confidently predict the plot right now: Maimed soldiers test new technology to get new bodies, bodies are used to infiltrate enemy ranks and then reveal position so the GI Joes and swoop in. However, while the soldiers are immersed in enemy culture, they discover strange and wonderful things, and realize the aliens aren't so bad after all, and now are conflicted between Duty and moral obligation.
There's probably going to be a gruff Alien chief who you wont like at first, but will turn out to be a pretty decent guy right before he dies, and if the main character doesn't fall in love with the alien chick, who's probably the gruff chief's daughter, I'll eat my hat.