Reddit reviews The Unanswered Question - Six Talks at Harvard by Leonard Bernstein

The Unanswered Question by Leonard Bernstein might be what you're looking for. I confess, I have yet to watch all six talks in their entirety but the ones that I have seen are very interesting. He delves into a "convincing discussion of music's history and forms, with particular emphasis on modern music" and covers a wide range of different composers. Read the review on Amazon for a bit more info.

Leonard Bernstein was a truly magnificent educator and musician. Unfortunately, the sound is already muted in at least one of the youtube links due to a copyright claim.

These lectures are still available to purchase on DVD (as well as in book form, though the video is more engaging). I have owned them since back when they were only available as audio on vinyl, and they are the most treasured element in my informal musical education.

http://www.amazon.com/The-Unanswered-Question-Harvard-Bernstein/dp/B00005TPL8/ref=sr_1_1

It's available here: http://www.amazon.com/Unanswered-Question-Harvard-Leonard-Bernstein/dp/B00005TPL8

[Leonard Bernstein - Young People's Concerts with the New York Philharmonic](
http://www.amazon.com/Leonard-Bernstein-Peoples-Concerts-Philharmonic/dp/B0002S641O/ref=sr_1_1?ie=UTF8&s=dvd&qid=1289508589&sr=1-1)

The Unanswered Question - Six Talks at Harvard by Leonard Bernstein