I like reading science fiction (SF) from time to time, though I can't say I'm a hard-core SF fan (I don't devour a SF book a week, don't attend SF meetings and don't try to write SF of my own). In light of this, "A fire upon the deep" is probably the most "hard-core" SF book I've ever read. It contains quite a few unusual ideas, some of which make more sense and some less sense.
What I liked the most was the Tines. This is truly the most original aliens race I've met in any book. Not your usual "everything like humans, just look like bugs/cats/cows" aliens. The Tines have group intelligence, and they act sensibly only in "packs" - individually they are not much smarter than dogs. The inter-pack communication is done via sound waves, and I must admit that I found the concept of applying radio to enhance it brilliant.
The other grand topic in the book is the "Zones of thought" - an idea that the laws of physics are different in different zones of the galaxy, and farther from the galactic center much more powerful beings can reside, and faster-than-light travel is possible. Now, here I go against most reviews - but I didn't really like this idea. Maybe it's just too bizzare, maybe the book doesn't explain it too well - I'm not sure. The bottom line is that I felt the "zones" discussions in the book hard to follow, and some of the chapters were nearly complete gibberish.
I always like to note how a SF book is affected by the time in which it was written. It also affects this book - though there's faster-than-light travel, super-AI-intelligences and dreadful planet-destroying weapons, what is the method of communication used between world ? You'd never guess - USENET. The book was written in 1993, certainly under the influence of the popularity of USENET back then. It was before WWW, before ICQ/AIM, before VoIP, etc. It's funny that creatures who move faster than light send newsgroup messages to each other :-)
All in all, I can't say I liked this book too much. I guess it takes someone more seasoned in SF reading to appreciate it.