Neptune's Brood

This story has a lot of great ideas in it, depicting a future with interstellar, but not FTL, travel and a number of characters radically modified from the original human form. The water world on which much of it is set is also intriguing, based in part on some real-world theories as to what such worlds may be like (i.e. a bit different to those in much standard sci-fi fare).

One of the main themes, however, is the financial system, necessarily adapted to vastly long travel times. The central character is a financial historian, dedicated to the study of a particular kind of fraud that forms much of the plot. As such, there is rather a lot of discussion of economics in the book - whopping great chunks of it at times - and it's these that prevent me from giving the book a 5/5.

It's undeniably inventive, and the plot is actually pretty good, with a fair bit of action and some good characterisation in amongst all the ideas, economic and otherwise. But it is, at heart, an “ideas book”, and, while I loved the science, how much you enjoy the book overall may depend in large part on how much speculative economics you're prepared to put up with.