Here is a shiur that Rabbi Triebitz gave during Chol HaMoed Pesach 5769 on the redaction and development of the Haggadah, and the real meaning of the Seder.
Unfortunately it is only available as an audio shiur, as I didn’t take the video camera to the shiur. But you can listen to the shiur here:
History and Development of the Haggadah
Download the shiur in mp3 format