At the time of this review, I have also read the 2nd book (Iron Sunrise) which to me was much stronger than Singularity Sky. There's a mix of great ideas and insights on the one hand and complete absurdity on the other. The main characters are likable and relatable, and feel like bona fide human beings. So when the action picks up and they're threatened, it easy to identify with them and get furious with their adversaries.
The Technology Singularity on Earth gave rise to a powerful collection of AIs known as the Eschaton. After the Singularity, they distributed 90% of the residents of Earth over many systems within 1000 light years. Despite their power, they don't really want to kill anyone. But if any party ever attempts to go back in time and change the events that led to the Singularity and their existence, beware! And if they inadvertently take steps in that direction, trouble awaits them.
The "light cone", causality relationships, slower-than-light (STL) travel versus FTL, time travel, and instant communication based on quantum entanglement are brought together in a fascinating and compelling mix. And I liked the idea of a cornucopia machine that can basically manufacture anything, but in this novel it seems more like magic than science. At the very least, it's a convenient plot device.
The Festival is a collection of uploaded consciousnesses that travel the universe to trade information for anything a cornucopia machine can make. Their presence and their effect raises hell with the civilizations they visit. But to me The Festival felt like a crossing from science to fantasy and then into complete absurdity. I found most of the passages regarding The Festival to be tedious and uninteresting. Though the idea of a race of infovores sounds promising, it just didn't work for me. The one fascinating aspect of them is that they are neither friend nor enemy, but even without friendly or hostile intent, their effect can be infinitely rewarding or devastating.