The light emissions from the lightning should be much brighter, cover a much wider range, and light up the sky as well as the ground like real lightning does.
I can not hear the thunder after seeing the lightning.
The lightning even set to max setting seems too infrequent, there should be an option to decrease the time between strikes. Also I think lightning should have multiple animation frames per strike and occasionally having 2 or 3 lightning strikes timed close together. I found a video of lightning recorded in slow motion http://www.youtube.com/watch?v=RLWIBrweSU8