Another excellent work by Sagan, this time the transcript of his Gifford lectures in the 1980s. The theme of the lectures is always 'natural theology', which for Sagan means touching upon science and astronomy, but also the aspects of those matters that have to do with religion and a sense of meaning in the universe.
His skeptic and scientific tone is present throughout, yet always respectful. In this sense, I would consider this work, and many of his other books (particularly 'Cosmos') as pleasant companions (or alternatives) to many of the more atheism-oriented books published today by writers like Dawkins. Sagan never compromises logic and science, and he's critical of many superstitious phenomena (religious or otherwise), yet he is always willing to see good in many things, including spiritual approaches to the universe, as long as they make sense.
A possible point of criticism might be that Sagan repeats himself at times over the course of multiple books. There's a lot in here that's also in 'Cosmos', 'Cosmic Connection', 'The Demon-Haunted World', etc. That's only a problem if you're a Sagan collector, though. By itself this book is concise, clearly written, elegant, and relevant.