Clean, engaging prose--no small feat with some of the ideas raised. And I love the conceit: examining a few conundrums which expose the way we're still trying to frame certain problems (in cosmology, biology, etc.). But I'm with Buck
in finding the first half more engaging than the second.
I came to this after I was pointed toward a discussion of the Wow! message (received or noted by SETI a couple decades ago). I found myself in that chapter wishing for much more on this particular problem, and I bet many people find their own preferred mystery -- it's a credit to Brooks that I wanted more expansive and deep-digging studies, 'cause I was finding his writing so effective at integrating research and anecdote and explanation. The end result can be like a series of snacks, rather than a meal. Still--I like snacks.