The trailer starts with a somewhat haunting version of the posters I remember seeing after 9/11, from loves ones trying to find there lost friends and family. The level of detail in these picture are amazing and are so random and varied that they perfectly linked together to form a beautiful yet haunting montage of lost souls.
The music is also key to the greatness of this trailer, it's a slow downed blues like version of "New York, New York" by who I think is Polly Scattergood (but I could be wrong about this) I have always like this type of piano driven music played of horrific images, they just seems to complement each other.
I do love how the aliens perform and surprise attack on the assault team and are vicious with them on the ground, only to be somewhat halted by a self sacrifice.