I've been an insomniac my entire life. When I was a toddler, my mother would put me down for a nap, and once she fell asleep, I would get up and play. When I was older, I was found sleep-walking. Life is just too intensely interesting to spend much of it laying down with my eyes shut. When I was made to stay in bed, I brought a flashlight with me so that I could read under the covers. So I was immediately intrigued by the concept in Beggars in Spain, of a society of Sleepless - people genetically engineered to be productive and awake 24/7.
Fifteen years after the first publication, Nancy Kress' Beggars in Spain, Beggars and Choosers, and Beggars Ride is still a mind-boggling rich tapestry of futuristic society, with deep characterizations, a plot that twists shockingly right up to the ending, and a piercingly accurate portrayal of thought processes and social dynamics.
The science is believable and has not yet been outdated, (at least not so far as this non-scientist could tell at any rate). It doesn't get in the way of the plot, and does generate musings on social and medical ethics.
Like Heinlein, Cherryh, and Orson Scott Card, Nancy Kress uses the contrast between familiar human society and alien society as a vehicle for raising the question of what, exactly, makes us human and what we value in a person or a society.
Beggars in Spain won a Nebula and a Hugo award. I give the trilogy my own highest honor: I'm keeping it on my bookshelf, because I will read it again.