For me it would have to be the Dragon Shout. Yeah I know it is one minor detail in an otherwise superb trailer however I couldnt help but feel that the shout in the trailer felt kind of weak. Now when I imagine Dragon Shouts I imagine that they would be performed by somebody with a very powerful voice, one that would shake the very foundations of the earth when the sound leaves his mouth somewhat like Christopher Lee (you can see why he was chosen to play Saruman) or Max Von Sydow but instead the actual voice actor comes off a little weak. Perhaps the other races will have more powerful voices however as I have said it is a minor issue in a superb trailer.
So what is your gripe with the trailer?
On a lighter note here is a video of Saruman being a dike that I found while trying to find an example of his voice.
http://www.youtube.com/watch?v=PTWkq1yo_YY&feature=fvst