In 1966, this shared the Hugo with Dune. It's hard to image such a slim volume sharing the limelight with today's heavyweight contenders, but the storytelling is still unparalleled. The depiction of an earth abandoned by the majority of the populous after a disastrous nuclear war plays as backdrop to the set-piece workings of the anti-hero (Conrad) with the long and ambiguous (and possibly pre-historic) life as poet, philosopher, terrorist, warrior and ultimately the protector of earth's past. How he then manages to become the defender of the off-world powers while dismantling the pyramids and getting involved in semi-mythical encounters, only Zelazny could pull off.
Conrad's initially indifferent involvement with the ensemble cast (including one 'Hasan the assassin') intensifies while he acts as loyal tour guide to a wealthy off-world alien who the local earth terrorists want to bump-off. In the midst of this, a personal bereavement and his own longevity play on certainties that were concrete at the start of the journey.
All this in about 174 pages of a first novel. The ending may be a bit trite, but I've no hesitation in recommending this - any other author would have jealously eked out the trove of characters and ideas over a series.