A rereading, this, but I remembered much less of it than I thought, and enjoyed it even more than I expected to.
All I really remembered in any detail was the dog-like pack-based beings, the Tines. Maybe a vague sense of the rogue superintelligent AI that caused all the problems.
And the “Zones of Thought” themselves, of course. A genius idea, which, in brief summary, is this: the further out from the galactic core you get, the more advanced the technology that is possible. Implicitly that includes biology. It’s never explicitly stated, but it seems likely that deep inside the galaxy, in the “Unthinking Depths,” intelligence is not possible. Further out you get the “Slow Zone”, which is where Earth is. Only sub-lightspeed travel is possible here, and machines cannot become intelligent.
But all this changes when you get to the galactic fringes, or the “Beyond,” where FTL and something close to AI are commonplace. And the further up the Beyond you go, the more this is true, until you reach the “Transcend,” where godlike AIs exist.
My memory was that the sections with the Tines were kind of annoying, with a sense of, “I want my space operas to be set in space, with high tech; not on a mediaeval-level world with nothing more advanced than cartwheels." But of course the story of the kids stranded on the Tines' World are both fundamental to the overall story, and at least as good as the galaxy-spanning main plot.
This book has gone from new, Hugo- & Nebula-Award winner to SF Masterwork in what feels like a very short time. It was first published in 1991, which is 25 years ago. I suppose that’s enough time to become a classic. The accolades are thoroughly deserved, of course.
The SF Masterworks edition has an introduction by Ken McLeod, which is well worth reading, and the whole is highly recommended by me.