In January, I ended up listening most to three albums: Philip Glass: Early Keyboard Music (new recordings of 60s compositions), Terry Riley's Shri Camel from the 70s, and Return to Forever(featuring Chick Corea)'s Where Have I Known You Before from the 70s.
The Philip Glass pieces are generally hard-core minimalism played on organ, the Riley is "loopy" minimalism played on altered organ, and Return to Forever plays jazz-rock fusion on electric keyboards (with guitar, bass and drums). To cope with the different but similar music, I placed them on a continuum from rigorous/hard/composed/serious to casual/light/improvised/fun. And Shri Camel falls exactly in the middle of that spectrum, neither too heavy nor frivolous.
The CD notes that Shri Camel is "composed and performed live-improvised" on an electronic organ tuned in just intonation with digital delay. That timbre plus the improvisational feel clicked for me.
For what it is worth, Keith Potter, in the book Four Musical Minimalists, points out that "shri" is an Indian term of respect, so in effect the title is "Mr. Camel." He also says this piece "represents the culmination" of Riley's works for electronics begun in the 1960s and marks the end of Riley's interest in pure minimalism. Reportedly, the group Piano Circus is recording the piece based on a notated version.
Samples on Amazon (click on the CD covers).