A good friend sent me Beggars in Spain about a year ago, and I enjoyed it, but not enough for a reread.
Kress is an entertaining writer, but she does not always give her characters the depth that they ask for, and I found her science to be less than believable at times. She falls to the trap of many science fiction writers and treats science more like magic in a fantasy book than like real science. It just happens. There aren't any magic wands, but there might as well be for the ease with which the characters tinker with genetics. A certain amount of suspension of belief is definitely required, but even then my logical side nagged at me as I read the book.
Perhaps my quibble with the science of the book would not be so large if the characters and plot had been more engaging. Amusing, yes, interesting, yes, a good way to occupy a few hours, yes. But at the end of it all, I was left with that telltale feeling of disappointment and longing, as if the author could have done a lot more with her plot and characters. I cannot help but compare the book to Octavia Butler's excellent "Wind Seed," for their basic plots, if not their settings, are very similar. In "Wild Seed," the characters are so engaging and fascinating that whatever faulty logic may have existed was made nonexistant in the face of the conflict between two superhuman beings. "Beggars in Spain" tried, but failed, to do the same.
If you read voraciously as I do, this is a good way to occupy a couple of hours. However, if you read less often I'd suggest you go for something with better quality than this, something that is great, not just okay.