This Immortal, Roger Zelazny.
This book is essentially about a middle-aged god - about a Pan who has become utterly apathetic. This is only hinted at, and contributes to the sense of the supernatural that is a bit atypical of the science fiction setting.
If anything, this book is sort of an anti-bildungsroman. There is absolutely no character development, and the plot ends because the protagonist is disinterested in the world and in development. I think this unsurprising given that the protagonist is meant to be an Overman (since an Overman need not change, being by definition the pinnacle of achievement). However, this makes the conclusion rather disappointing, as there is no real conflict in the first place, and hence not much need for resolution.
I would very much like to read Zelazny’s other books though; Lord of Light is supposed to be much better.
