I really enjoyed the album. I found it to be far-reaching, ambitious, organic, a bit untethered, intellectually challenging. But that isn't all. It was unusual, and groundbreaking in its context of the late 60's/early 70's. Like Tago Mago by Can, this album exists in its own space, seemingly without contemporary Rock influences. At the same time, it floats in and out of various influences like free jazz, avant-garde classical, psychedelic rock, and (contradicting myself) rock as well.
Like this review, the album is long. It consists of four pieces, one on each side of a two album set. Each piece has its own cycle. These compositions remind me of classical, which is why I referenced that form earlier as an influence. The structure of the music is more classical than the actual instrumentation, which is the familiar drum/bass/guitar/keyboard of any other rock band of the time. Whitin each piece are parts, and often a reprise, like an Opus consisting of several parts. Most classical music that I've heard does this.
And Soft Machine explore uncommon time signatures you don't find in popular rock music, or really classical. Jazz? perhaps Take Five by Dave Brubeck. But Soft Machine go hard in the paint on the 5/4 and 7/8 stuff. They also juxtapose patterns in the rhythm section that I'm still trying to figure out/. Is it 9/8 and 4/4 back to back? Or is that 10/8? Again, intellectually challenging.
So these things - the relationship to classical music and playing fast and loose with the time signatures are the defining elements of Prog hereafter. King Crimson was attempting things like this at the time, and "Robert Wyatt's "Moon in June" could be a Genesis song. Nonetheless, Prog rock as we know it now starts here. It's not particularly well mixed. The drums are really flattened and pushed to the right channel for a lot of it, the keyboard can become shrill and overwhelming. Even with those faults, this is still an intriguing piece of work with some depth and artistic risk-taking that helps define the genre.