Prophets of the Ghost Ants by Clark Carlton, I made the mistake of "taking a quick look." Since I'm just getting back into flying this summer after a few years away, I've really been trying to focus on study for my flight review, but I kept getting sucked back into this book instead! I really couldn't put it down (and since I was reading it in the Kindle edition on my iPod Touch, it was always at hand).
I'm not usually a fantasy reader (I tend to go for "hard SF"), but this book is somehow in a strange zone that is not quite fantasy, not quite "hard" science fiction, but is "sciencey" enough to reward my suspension of disbelief (great storytelling and characters helped too). The last time this happened was with a book Amazon was giving away as a Kindle loss-leader, His Majesty's Dragon by Naomi Novik. I was skeptical because dragon books are generally pure fantasy, but it was no risk to try. In that book, Novik re-imagines the Napoleonic wars with air power - flying, intelligent, talking dragons that crews of men ride into battle. The historical fiction is played straight (like a naval history novel), and the dragons are simply folded into that world (with great relationships between the dragons and their crews, especially their captains). That worked well enough to sell me six sequels! I think Carlton's "ant world" will be equally fertile (despite a similar disregard for physical scaling laws - dragons as described would be way too heavy to fly, and ant-size humans? I don't know, but it works in the book!).
Some Amazon reviewers have mentioned The Lord of the Rings, and I have to agree that the scope, world-building, compelling characters, and action/battle scenes of this book are of that quality. There is also the "unlikely hero" angle - but otherwise the stories are completely different. And although it's not hard SF, the biology of ants and other insects is an important part of the way these tiny human societies work, and it seems to be pretty accurate (and occasionally disgusting). There's also a tremendous amount of cultural anthropology embedded in this book - not in a scholarly way, but in an Ursula Le Guin sort of way. Under these circumstances and constraints, what would societies be like? What would their folk ways be like? Carlton has clearly thought a lot about these things, and they give the book an amazing depth and richness.
This is a great book. I can't wait for the sequels (and the movie!). Highly recommended!