So, the galaxy is divided in four layers more or less based on the distance from the galactic core. The further you get from the core, the more advanced your species is and can be. For reference Terra is in the Slow Zone, between the Unthinking Depths and the Beyond, far from the unimaginable Trancendence. Some human civilizations have made it to the different levels of the Beyond, which is also divided into low, middle and top levels with variance in the technology levels. One of them has managed to travel to the highest zone and pokes with things they don't understand, releasing some Ancient Evil.

The fun trick is that the higher-level tech doesn't work in the lower level zones, so the superfancy FTL and natural AI breaks down or just simply stops working in the lower zone, leaving the advanced folks stranded. The species living in the higher levels also don't really care about the lower zones that much, as they've got their appendages full of everyday work in their own level, maybe slowly working towards leveling up.

One of the things I greatly appreciate in Vinge's writing is the lack of exposition. Yes, that makes getting the universe a bit slower, but I enjoy that much more than infodumps. I also have read Vigne's A Deepness in the Sky before this, so a couple of mysteries were spoiled already. This didn't negatively affect my reading, anyway, so I imagine the reading order is unimportant.

This is a fairly long novel of ‘hard science fiction’, but it is well-paced and kept me wanting to read more.

The characters are diverse and well-rounded, and the dialogue feels realistic among and between humans and alien species.  Although its action has a galactic sweep and the story has a backdrop of aeons, the reader is drawn into the fate of the central characters, ethically good, bad and doubtful, both human and alien.

The overarching framework is one of a negative quest, oddly reminding me of The Lord of the Rings, but as SF not fantasy. The structure of the galaxy portrayed and discussed is reminiscent of the tiered worldview of the ancient world (heaven, land/sea, underworld), which adds an interesting complexity to the action as well as a rationalisation for a certain degree of deus ex machina.

One peculiar omission from a novel of such broad outlook is the total absence of any religious belief or motivation, either within a now-widely scattered humanity or among alien species. Even for hard SF, for a story of such a wide outlook I would expect it to occur at least as an epiphenomenon.

The novel was originally written in the 1992, and the flavour of the galactic Net is endearingly evocative of the Internet of that time.

Space adventure, very cool characters. Robotic millionaires, technological demons, friendly plants, psychologically fascinating dogs.