Let over Lambda is an exploratory journey into advanced techniques involving Common Lisp features and language properties, that can be combined in ways that result in more than the sum of their parts.
There are plenty of "wow, that is cool" moments and useful constructs demonstrated, that will probably make it into the reader's toolkit. But of greater importance is the progression in how these are delivered. While not a broad tutorial in Common Lisp (although the reader-macro chapter could serve fairly well in that capacity), Let over Lambda contains an underlying tutorial on the incremental/iterative development of such macros/tools against desired requirements - building up to constructs via interim revisions and explanations.
A book involving Lisp has little choice but to stand on the shoulders of giants, and by necessity these are frequently referenced and cited. The most important of these is Graham's "On Lisp" (currently available for free download) - which, while attempting to cover the breadth of the language, is regarded as one of the more advanced texts on macros. Some topics introduced in On Lisp (such as the leveraging of unhygienic macros) are taken much further in Let over Lambda, and combined with other constructs (such as capture/closures) that would have to be described separately in more general purpose tutorial or language overview.
The writing style definitely includes an "attitude" that is partially inherent to the material being discussed and partially from the author's obvious passion (a passion that becomes REALLY obvious in the Forth chapter). Hoyte often highlights the blanket superiority of Common Lisp over all other languages; but to a reader who has put in the time to learn Lisp macrology in enough detail to understand this book, this isn't a particularly large stretch. Also, certain comfortable safety idioms are challenged as being more safeguards for beginners. On several occasions, the reader receives an explanation: "Here is the what and why of adhering to restriction X. Now here are the incredible things that become possible when you break it!" This is demonstrated via unhygienic macros, as well as the broader concept of "duality of syntax" - a definition that evolves throughout the book.
Early in the introduction Hoyte states that macros (in a language that can leverage them) are more than just boilerplate-reduction tools for known simple cases; but that their power represents a sort of "uncharted territory" of immense potential. Certain common (seemingly) ideological arguments (things like lisp-1 vs lisp-2), were laid out against a backdrop of examples and threaded into the theme of the entire book. While often going out on a limb, the author makes his case.
I was inspired by this book.