King Crimson - In the Court of the Crimson King
Score reading along with it. It's kinda interesting to see how prog has...well, progressed since this album. Like, the use of time signature changes in prog slowly got more complicated (I score read some Yes songs just before this, and they're more metrically complex than King Crimson is and DT...well, you can imagine). A lot of the trends that defined how prog uses meters were established very early on from what I can see, it's just that each generation of prog bands pushed the boundaries a little further. In the Court of the Crimson King, for example, has time-signature changes in the low double digits while every DT album has somewhere between 180 and 600.
But on the other hand, there's a lot less counterpoint and stuff going on. A lot of things that seem to be common place in early 70s prog just seems to be gone now. The harmonies of bands nowadays are a little bit simpler (not bad tho, they just decided to focus on different things) and the ridiculously dense counterpoint of bands like Yes and KC are gone. The free improv stuff and S P I C Y note choices that KC used a lot seems to have been dropped really quickly too (I'm not too sad about that tho). The tempo also seems to have picked up a lot since the early days, because most of the songs here would be considered ballads now. I think it's interesting how much progressive metal shifted the focus from harmony/form/counterpoint to rhythm/form/meter to incorporate the new rhythmic influences.
Anyways that's my musings. There's a lot of good stuff in this album and a lot of things that I wish had caught on in prog in general (and some things that I'm VERY glad did not).