"Unformed and Unfilled" is a critique of the gap theory (the idea that there's a large gap in time--usually between Genesis 1:1 and 1:2--between God's original creation of the universe and a re-making of the earth after a world-wide flood upon the earth done in judgment of Satan's rebellion). The author was very thorough in his explanations of why the gap theory (in its many variations) isn't consistent with the Biblical account, especially when studying the original Hebrew words and grammar. His writing was more formal in tone and required anyone not familiar with Hebrew grammar to learn a lot about it from this book. However, it was written clearly so that his arguments were easy enough to follow.
The author covered the arguments given for the gap theory in great detail so that highly-read believers in the gap theory will understand his points. However, someone who doesn't know that much about the arguments for the gap theory could get overwhelmed by all the information and miss the really critical points. Still, I'd recommend this book to those who hold the gap theory or day-age theory (though books with more scientific evidence for recent creation might be more effective) or those who want to know the Scripture-based arguments for why those ideas don't work.
The author covered what the whole Bible has to say about creation and its timing, ancient Jewish interpretations of Genesis 1:1-1:2, and early Christian interpretations and post-"long-age-geology" Christian interpretations of Genesis 1:1-1:2. He gave a detailed explanation of the grammar and linguistics of Genesis 1:1-1:3 (mainly, bara/"create" and asa/"make"; what type of sentence is Genesis 1:2; the waw type; "was" versus "had become" or "became"; and tohu/"without form/shapeless" and bohu/"void/empty"). He also covered the lesser arguments of 'Genesis 1:2 had darkness, but God is light,' "framed" in Hebrew 11:3a, pre-Adamic men, and Lucifer's flood.
Finally, he covered other long-age creation theories: the dependent clause interpretation of Genesis 1:1 ("When God began to create...") and the Day-Age theory. He described three types of apologetics along with why he believes nothing is really gained by compromising Scripture to make it appeal to people. He concluded with a very brief explanation of (Noah's) flood geology as an explanation for fossils, etc., and two scientific evidences for recent creation (the Earth's magnetic field and radiocarbon dating).
I received this book as a review copy from the publisher.