Cincinnati.com reviews Glass' opera Galileo. The criticism of the score preventing the opera from succeeding reminds me of Gian Carlo Menotti's comments about his operas where he says (in french) "I'm accused often of creating too much theater and not enough music. I think that to accuse an opera composer of creating too much theater is like accusing an poet of writing too much poetry and not enough literature."
Something must be working for Galileo and its merits as a piece of theater. It's one of Glass' most often performed operas now having its tenth production (most operas by living composers are lucky to get performed more than once).
Similar comments revolved around the major Glass revivals like Satyagraha at the Metropolitain Opera and the English National opera in 2007, '08, '10, and '11 (and now fall 2013 at ENO). When faced with what I think was an inspired restaging with orchestras and singers of the highest quality, the critics refrain was often "Ok, ok I get it. It is a wonderful piece of theater but just not very good music." This is total denial that the stage work and the music are part of the same poetic message. But let them have it their way as production after production gets mounted.