Late's perception of Riley is spot-on, especially the Crispell connection (I think I made the same reference in a review of a disc by the Guy/Crispell/Lytton trio).
It's interesting to hear the progression of his music across the trios in the '60s/early '70s - always with Barry Guy, and Jon Hiseman, Alan Jackson and Tony Oxley occupying the drum chair. The electro-acoustic improvisation of the Oxley years is great, but I have a fondness for the structures of The Day Will Come (Guy wrote a lot of the pieces there) and the supple-yet-agitated swing of Discussions, his first as a leader.