Absolutely wonderful. Though none too prolific, Ted Chiang is evidently a writer of incredible talent. Chiang writes very powerful short fiction based upon a hefty scientific foundation, whether it be mathematics, engineering, psychology, linguistics, etc. Unlike much other science fiction, his stories are markedly grounded in a realism that makes them very relatable.
His brilliance is most evident in his ability to take fantastic ideas (a tower that reaches the vault of heaven, acquiring superhuman intelligence, contact with aliens, and a world in which angelic visitations are not an uncommon occurrence, for example) and build innovative and realistic scenarios around them complete with very human characters. What I like most is his approach of going in-depth on the scientific principals behind the scenes and their consequences, while still being compelling reads. Though the ideas explored in his works are usually quite complex, his prose is clear and never comes off as overwrought.
This collection of stories stimulated my cerebral cortex like few others. Personally my favorites were the stories in which Chiang experimented with religion, The Tower of Babylon being one of the best stories I've ever read. But they're masterworks all, you can't go wrong. I would compare Chiang to Borges for his seemingly effortless ability to weave such profoundly thought-provoking stories.