I think he pioneered some techniques in storytelling in film such as having multiple threads of different storylines woven through each other (people told him he couldn't do that while he was making Amercian Grafitti, now it seems like a lot of people are doing it).
Obviously with THX he helped make the movie going experience grow into the subwoofer driven, multi channell surround experience we take for granted today.
I also think that with the money he had dumped into digital cameras and digital presentation, he is again dragging the industry towards a higher standard of presentation in general.