This was actually my second attempt at reading this book. When it first came out, I picked up a library copy, but after a handful of pages the use of what I thought was invented dialect turned me off. Later I learned that the dialect was actually Caribbean English, which made it seem part of the story instead of self-indulgent affectation. With this in mind, I began to read Crystal Rain a second time.
The premise: John DeBrun is an amnesiac with a past. When bloodthirsty Azteca boil over the mountains and begin sacrificing and conquering his people, he must do what he can to stop the assault, even if that means regaining the memories of his lost life.
The twist here is that both the Azteca and their peaceful neighbors are descendants of colonists from Earth, and both societies worship aliens who have taken the names of Earth gods. The war is in some sense a proxy war between two alien factions, although that makes it no less deadly to the humans.
Another twist is that some of the people are "oldfathers": people with modified bodies and nanotech blood who have lived since humans arrived in the system hundreds of years before. They may be able to make a difference in the fight, or their long lives may have made them so risk-averse as to be cowardly. The oldfathers could have been used to explore some interesting problems a la Lazarus Long, but this is only briefly alluded to. (It does seems unlikely that one of the most famous fighters in the original alien conflict could reappear hundreds of years later and not be immediately recognized by any of the aliens or oldfathers who were alive the entire time.) Kudos to Buckell, though, for resisting any temptation to make the oldfathers all-knowing, kind, and wise. A randomly selection of people given almost eternal life would probably include a hefty share of ignorant cravens and mercenaries.
The Azteca in general interested me, and I want to hear more about them. For instance: how was a dead Earth religion imported to a new planet, adopted by aliens, and embraced by humanity? The character of Oaxyctl, an Azteca spy, is the only one with a significant internal conflict to face, which dims the relative appeal of the protagonist; De Brun's motivations are fairly straightforward, as with most action heroes.
Crystal Rain is perhaps SF's first example of Caribbean steampunk, and therefore a genre unto itself. If you are in the mood for something that's a little bit Star Wars and a little bit Bourne Identity, but with a dreadlocked version of Wolverine thrown in, this book is for you.