When I re-read The Sparrow in the spring of 2010, I knew that Children of God would get a re-read not long after. My recollections of CoG were much less vivid than those of The Sparrow, for one thing, and I wanted to refresh them; for another, although CoG is a follow-up to The Sparrow, I consider the two books as a single story, and forgoing the second part of that story wasn't an option for me.
Children of God opens shortly after Emilio Sandoz has responded in full to the Jesuit inquiry about the original mission to Rakhat, and one outcome of that response is that the Jesuits want a second mission to Rakhat; that's the last thing that Sandoz wants to have anything to do with. His experience on Rakhat profoundly changed Emilio...but we'll learn that he and the other members of the Stella Maris crew profoundly changed Rakhat, too.
Rakhat and its people - the ruling minority Jana'ata and their partners and prey, the Runa - receive most of the author's attention in Children of God; while Mary Doria Russell introduced their world in The Sparrow, she builds it here. The themes of this novel are more political than philosophical and theological, and the questions it raises are different, although not of lesser importance. And while many of the new characters in this story are from other species, they are drawn and developed in recognizably human ways.
Another reason I wanted to re-read CoG is that I hadn't liked it as much as The Sparrow when I first read it, and I wanted to see if that still held. Granted, there are very few books I love as much as The Sparrow, which received a rare 5/5 rating from me. And while I liked and appreciated CoG more on this reading, I still like The Sparrow better. This is strictly opinion - I don't think I'd say one novel IS better than the other, but depending on your literary preferences in general, you might not like them equally. While both tell a fascinating story, I don't get the sense of intensity from Children of God that I do from The Sparrow. Also, CoG, with its heavier story focus on the denizens of another planet, feels more rooted in traditional science fiction to me, and I'm not a huge fan of reading SF. I prefer SF as a movie and TV genre, which allows me to see the world being created; I remain frustrated that I can't visualize the peoples of Rakhat. And while it's not a major issue - for some, I'm sure it wouldn't be a problem at all - it gets in my way, I'm afraid. I wish it didn't.
I'm very glad I re-read Children of God; I got more out of it this time around, and I have a greater appreciation for Mary Doria Russell's talent and accomplishment in creating this story. I still don't feel that it stands on its own as well as The Sparrow, but I have more recognition of how my literary biases influence that feeling. I will continue to recommend reading it along with The Sparrow, but if I could only read one of the two, I'd still choose The Sparrow.