This, like The Zenith Angle, is a slightly silly book. I'll take that back. It's nothing like as silly. It's slightly whimsical. The universe is of a fairly standard post-singularity, FTL-travel (but with relatively hard science despite that), uploaded-humans and nanotech type, with a neat little anthropic principle twist. The central civilisation of the plot is deliberately backwards, and is attempting to fend off a rather whimsical "enemy" it can't comprehend. It's all pretty fun, and treats sci-fi as a metaphor for computer science, like a rather weak version of Vernor Vinge. In particular, it's a rather simple allegory on the nature of the internet. While not the best thing ever, it's hooked me into looking out for more of his stuff.