Touching on concepts of evolutionary mental development the "Eth" has the ability to wish realities into being using the power within a galactic "psynergy" Sumner Kagan is an excellent anti hero, the book introduces many genuinely new and original concepts and creatures against a backdrop of a post apocalyptic Earth 5,000 or so years hence.
I have read and re read this book many times and get something new out of it each time. One of my favourite books, very underrated, try it you wont be disappointed