It still worked for me. Zelazny's writing in the first place is vigorous and powerful, and funny also on occasion; it is rather easy to get swept along by the characters with superhuman, semi-divine abilities trying to outwit each other without concentrating too much on the plot. His trademark was always the juxtaposition of the mythic and the demotic, and Lord of Light probably is the peak of his powers at novel length.
The plot also stands the test of time. The rulers of the world of Lord of Light have chosen to construct a religion in order to stay in power, and rather than make up their own (as later Zelazny books do) have taken Hinduism off the shelf, as it were, suited as it is to their reincarnation technology. "Accelerationism" (ie modernisation) among the general populace is ruthlessly repressed. Our hero, Sam, is one of the privileged who rebels, and uses methods of terrorism, war and assassination to undermine the power structures, is captured, executed twice, and eventually returned to life (at the start of the book, most of the story being told in flashback) and victory.
It's not terribly clear that Sam is doing this out of an egalitarian or libertarian commitment to oppose tyranny; it seems more that he (along with Zelazny) favours two different types of enlightenment - personal enlightenment in the (explicitly) Buddhist sense, and cultural enlightenment in the sense of eighteenth-century Europe, in both cases implying freedom from religious dogma and control, and so is committed to bringing them about.
To achieve this, he has to do a deal with the indigenous entities of the planet as well, now known as the Rakashas; he exploits them but also possibly liberates them, and their support is crucial to his ultimate success - a subplot with interesting undertones both historically and psychologically. Note also that the explicitly Christian characters are dubious outsiders who are minor but somewhat unreliable allies (leading an army of soulless zombies). Plenty of cultural irony, directed mainly westwards.
Lord of Light won the 1968 Hugo Award for Best Novel. Other shorlisted books that year were The Einstein Intersection by Samuel R. Delany, and three books I haven't read: Chthon by Piers Anthony, The Butterfly Kid by Chester Anderson and Thorns by Robert Silverberg. All except the Anderson book (of which I have otherwise not heard) were also shortlisted for the Nebula, which was won by The Einstein Intersection.