I'll be reasonable.
The only thing I hope for is a live action halo 4 trailer, so i have something to watch on youtube a few dozen times. Its crazy how great the ODST and Reach ones were. Comparable production values to the big hollywood blockbusters.
While gameplay footage would be nice to see how the game is going and all its not really something that will have a wow factor like battlefield 3 gameplay or god of war 3 gameplay. Halo games are fun to play not to watch be played like the before mentioned games, so it will be hard not to be dissappointed by a gameplay trailer.