This is an exceedingly interesting experiment, producing many fine moments. For me, the alternating first sections gave rise to the best music. The latter sections, while very clever mentally and aurally, with simultaneous playing, I feel serve to show the limitations of parallel improvisation. I am just guessing really, as I have never actually tried this sort of thing myself. However, even if the form were very obvious and the aural acuity of the participants exceptional, truly free, spontaneous creation, with organic form but no a priori structure, is essentially the product of one mind. That is not to say that multiple improvisation cannot have quality, it is after all what jazz groups do all the time, and it is very highly skilled.
Alternating improvisation, where each player might use some features of what has gone before, while retaining individual freedom from the temporal prison of simultaneous playing and structure, strikes me as very likely to produce vital sounds, as indeed it has here. I now have a desire to try it out for myself.
So overall, alternating improvisation yes, a brilliant notion; simultaneous improvisation no, rather too musically restricted for my taste.