IMHO, the only truly great work by Glass is "Einstein On the Beach", everything else is either an approximation ("Satyagraha", the other operas, film scores and the symphonies), a preparation ("Music in Twelve Parts"), a pastiche ("The Photographer" [but a good pastiche!
, or a failure (just about everything else). To be fair, his last two or three string quartets are OK.
LMG