‘New wave‘ SF came out of the UK and birthed a multitude of sub-genres we see today, cyberpunk, steampunk etc. It had its peak in the late 60’s and was established by Michael Moorcock. He hated the John Campbell pulp of the genre and legitimised SF and Fantasy into a literary form.

Michael Moorcock was an editor for New Worlds Science fiction and moved away from the John Campbell (US Analog SF and Asimov SF Mags)and John Carnell (UK New Worlds before him)

Roger_Zelazny was one of the first of the ‘new wave’ SF Writers whose ‘This Immortal’ book came second to Dune at the Hugo awards in 66. At the time it was considered cutting edge. It hasn’t aged well but is an excellent example of the ‘new wave’ writers and also the beginning of myth being employed in modern SF. 

This is a good review of the plot from TOR  books.

This is another good review from a journal this goes into the mythological background of the novel.