I have always been interested in the rather old school sci-fi, like Lewis's Space Trilogy and such. Back when there was very little character development and the protagonist existed as a vehicle for imagining a world vastly different than our own. Lindsay's book is very much in that vein; an exploration of what it means to be human using aliens. He has the bright idea of creating humanoids with extra sensory organs that mutate throughout the story and are used to explicitly display that which we can only infer. Lindsay's theories are fascinating, if very bizarre, and he at least does not fall into the trap of having a clear and obvious moral.
This was read at C.S. Lewis's recommendation and I'm not sure whether i enjoyed it or not, but I was enthralled by it nonetheless.