There are eleven distinct sections, each based around a single metallophone melody. Reich had previously used small ensembles and primarily layered patterns for rhythmic effects. Here, however, he used a large ensemble to experiment with harmonics and layering different harmonies and timbres. The effect he creates with choral parts gradually fading away is particularly interesting to me.
For me, the most striking thing about minimal music is how completely different it is in goals and executions from the mainstream of contemporary classical music, which is still based around serialism and aleatory (chance) music. Minimalism, rather than avoiding tonality and, let's face it, being deliberately impenetrable and difficult to listen to, experiments with effects that sound very familiar--the music is generally tonal, and the rhythms are simple, if complexly layered. It has immediate appeal and it produces an emotional impression (I think the latter is the point of music and exactly what is missing from Schoenberg, Cage, and so on).