Alex Ross (you might know him as the writer of "The Rest Is Noise" and/or "Listen To This," both excellent books that are informative on music and it's reception) has a great post on Philip Glass. It's Glass's 75th birthday and the premiere recording of his 9th Symphony has just been released: both reasons to re-visit his music.
I first heard Glass's music at university: I found a collection of piano music by a composer I heard of, but had never heard. Maybe I was fresh from reading Andrew Ford's excellent book "Illegal Harmonies." Who knows.
I remember putting the CD on and not understanding it at all. Why didn't the music do anything, progress, or move beyond the most obvious of materials? I listened to it for a week and abandoned Glass. Unfair, parhaps, but I was deep into jazz, and only really wanted to listen to notated music to absorb some "different sounds."
Recently I've become more interested in music and it's social function. Glass seems firmly in the category of composers who adopts a social function by explicit adoption of social elements: themes seem to often be from current affairs and world events. One advantage of this approach (as opposed to Adorno's view that music best displays a social function by becoming autonomous) is that it is easier for the listener to make sense of the sound. This is crucial if music is to avoid being cut-off from the society in which is exists. It's not a capitulation to 'dumber' audiences but simply an acknowledgment that music cannot demand people 'understand' what composers of autonomous music often proclaim as self-evident truths.
An interesting thing about Glass is that his musical materials remain similar: minimalism is, for him, material enough for social commentary. Hence Ford's quote from Wallace Stevens: "One sits and beats an old tin can, lard pail. / One beats and beats for that which one believes."
This could refer to musical materials as much as approach. I for one am planning on re-investigating Glass. It seems my earlier judgment might have been on the wrong terms.