Stay away from Children of the Sky unless, having finished Fire Upon the Deep, your response was "I'd sure like to hear more about those whiny children and the dogs"
It has been a while, maybe I'll give it a re-read at some point.
See my other comment up-thread ... what I really want is the opposite of this. I want the battling civilizations beyond the void memes all fleshed out. I want more details on how the civilizations "ascended" beyond the (whatever the demarcation point was). I want more details on how they came back on "our side" of that point and what it means and what their motivations are, etc.
Those are the plot pieces and background that are never fully fleshed out in Upon the Deep that make me rate it lower than In the Sky.
Let me also say ...
I have never played Mass Effect but there is a fascinating and deep backstory and created universe for that game that I find interesting and terrifying in the same ways I am interested in, and terrified by, the Vinge books:
"The Reapers are the original creators of the Citadel and the mass relay network. These massive constructs exist so that any intelligent life in the galaxy would eventually discover them and base their technology upon them – all part of a scheme to harvest the galaxy’s sentient life in a repeating cycle of purges that has continued relentlessly over countless millennia. "