This is a great book, but it will cost you. Right after I finished reading it, I ordered three or four books from its featured authors right away, and put several more on my wishlist.
As to how length and time are relative, this book is its own highly distinguished example: the excerpts from scientific fields I know next to nothing about were much too short, while those from scientific fields I have a little more knowledge, or had even read the books the excerpts were taken from, were much too long. So there.
For this book, Richard Dawkins did not merely write some plain old foreword, but introduced each and every author and excerpt, with background knowledge and sometimes amusing, sometimes thought-provoking anecdotes.
One peeve, though, and not an unexpected one: these far too long, and far too annoyingly unfunny excerpts from the writings of Peter Medawar. (I tried at times, at RDSF forum discussions, to disabuse Richard of at least some of his more outrageous notions about postmodernism, to no avail.) But, shortly after the Medawar Annoyance, everything was made up for by an equally long, carefully chosen, and wonderful essay by Stephen J. Gould.