I don't know all of Philip Glass' music. I don't know if such a thing is possible. I don't even know all of his operas.  Clearly it's only possible to know the commercially released ones plus perhaps a lucky chance at a live performance. In fact, many Glass operas which have not been recorded continue to get many performances including 5 productions last year of "The Fall of the House of Usher," and upcoming UK tour of "In the Penal Colony" which also had recent performance in Lyon, Rouen, and Paris in France.  I have a fond memory of the premiere run of "The Sound of a Voice" in 2003 , an opera I hope makes it to CD someday. 

Though us Glass fans have to be thankful for the now 12(?) Glass operas which have been released. Among them, like many other fans I find the original trilogy of Einstein, Satyagraha, and Akhnaten perpetually rewarding while some pieces like The Voyage I feel are good but not great, then there are some like Hydrogen Jukebox which I honestly hardly ever revisit despite their bright moments.  

Having said all of that, Waiting for the Barbarians is among the best operas Glass ever composed.  Based on J.M. Coetzee's 1980 novel, the story was incredibly poignant in 2005 with the American wars in Iraq and Afganistan which continue to this day.  The story is about a small village on the fringe of "Empire" which seemingly lives undisturbed in its backwater provincial state.  The Magistrate of the town is the main character.  He's sort of the main authority in the town which has its own system for surviving and operating. The story starts with the arrival of black coated "representatives" (thug G-men) from Empire.  The Magistrate begins the story with baritone Richard Salter's wonderful voice singing Christopher Hampton's libretto: "In fact, we never had a prison in this town, never needed one…"

Basically, the Empire comes in, paranoid about the "Barbarians" whom we never really see. They generally seem to be peaceful nomads but they are portrayed to be "the enemy."  After the goons take over the administration of the town, as a gesture of rebellion the magistrate takes in a barbarian girl who has been tortured by the empire's officials.  Her ankles were broken and a hot poker was taken to her eyes. Her father was also killed.  This 1980 novel, to which Glass got the rights to make an opera of it in 1990, took 15 more years to get to the stage. And even then it was a German stage as no American company was interested in commissioning this work.  It only seemed worthwhile with America's escapades in the middle east against the phantom enemy against whom we are still fighting today.

Coetzee and Hampton's words are plainly creepy and prophetic: "Normally speaking, we would never approve of torture, but I think it's widely understood that this is an emergency" and "a short sharp war to safeguard the piece."  For me, this opera was one of the only consolations against what was an impossible political situation in America in 2005 which in many ways continues today though we seem to have ceased the open practice of torturing prisoners.

Glass' music for Waiting for the Barbarians is inspired.  The tone is set from the beginning with a wordless chorus in the pit singing with the orchestra. By virtue of the orchestration we are immediately planted in this far off land "on the fringe of Empire."  The score is greatly varied and represents a wonderful refinement of ideas that Glass had been working on in preceding scores.  A great example of the violence and variety of the score, one should listen to Act I – Scene 9.  

In the scene, the Magistrate argues with Warrant Officer Mandel.  Mandel announces "a great offensive..to demonstrate our strength to the barbarians." (shock and awe)  It goes from the opening violent music at the beginning to the magistrate speaking nostalgically of his time years ago in the capital city of Empire. Mandel asserts that the war will make the barbarians fall in line. The magistrate rebels: "They want to roam through their ancestral lands in Freedom."  In the moment which frustration drives him into sealing his own fate, the Magistrate says:

"Sometimes I wish they'd unite and rise up, and teach us to respect them, Remember in their minds we are invaders, they think they have the patience to outlast us." 

Act I – Scene 9, Waiting for the Barbarians