I think a unique quality of it is the contrast between it's simplistic harmonic content and it's constantly modulating structure. The simplicity of the tonality (one key center, very slow chord changes, non-florid counterpoint) allows the listener to focus on the modulating phrase lengths and the texture of the stacked rhythms.
This is an interesting inversion of something like, say, a classic bebop tune, which might be melodically and rhythmically complex or divergent, but keep it's structure predictable with 4 bar, 8 bar, or 32 bar chunks of time.
I think the effect in it's fast movements is like being in the middle of a massive rush of water. It's uniform in texture, but it has an intensity and sense of turbulence that is overwhelming as it passes you.
It’s a wonderful experience with a nice pair of headphones. Something about the way the repetition lasts just long enough to produce a sense of anticipation and delight.
It seems that there may be a quality to his music that makes it well-suited to working.
Anyhow, I didn't know that either about his life. Very fascinating.
As an aside I believe I discovered Einstein on the Beach after listening to Hydrogen Jukebox. I wonder how others come about listening to it for the first time. Especially those in their 30s like myself who were born a decade after its success.