Both science geeks AND "soft" SF fans will love this!
Nest of Worlds creates a fully realized alternate world that has its own physical laws and societal mores. It's also a metafiction: there are layers of nested stories, each of which appears in a different font. Readers who like "soft" SF a la LeGuin will enjoy the exploration of the stratified societies in both the main story and the nested ones (it reminded me a bit of The Dispossessed). But readers of hard SF will enjoy the exploration of the physics (science geeks will really love the detailed description of the physical laws governing the nested worlds). In addition, it's very well-translated by Michael Kandel, the translator of many of Stanislaw Lem's novels into English. In short, there's something for everyone in this book, at least everyone who's looking for a thought-provoking yet thoroughly involving read.