Outside of the casting, the Green Lantern suit looks more like reptilian scales than a suit. When the trailer shows the transformation of Hal Jordan in front of the window, the suit has a off-coloring that gives me the impression it was done in post rather than being worn by the actor. I'd rather see Green Lantern in a nipple-less molded suit than with a CG afterthought.
I am hoping the action will be bigger. The only fight scene the trailer gives away is Hal Jordan getting beat up in the parking lot and he realizes the ring can do something. In addition you can see him do a diving kick similar to something from a bad wire-fu movie. I don't know much about the action portrayed in the Green Lantern comics, but I'm definitely hoping for a helluva lot more. I don't want it to be as weak as Superman Returns was on action sequences.