I love biochemistry and microbes, but I didn't love this book. I found it tedious and somewhat superficial, which was surprising considering the amount of interesting information contained within the pages. I also did not learn as much new "stuff" as I had hoped, since most of the contents I have come across in other books. Life's Engines would probably function better as an introductory text to the subject, but may also be too complicated for readers who know nothing about things such as electron transfers, nitrogen fixation, ATP and genetics.
I found that the following two books dealing with microbes appealed to me more than Life's Engines by Paul G. Falkowski:
The Hidden Half of Nature: The Microbial Roots of Life and Health by David R. Montgomery and Anne Biklé;
March of the Microbes: Sighting the Unseen by John L. Ingraham,