This was a tough one ..
Which is a pity since it contains some very interesting stuff about macro programming.
So what's in the book?
It is a book about Lisp but neither an introduction to nor a reference. It is focused on macro programming. On the way there it starts by talking about scope and closures, followed by increasingly advanced macro topics: extending the language, extending the parser, macros that build macros, interaction of multiple levels of macros and macro efficiency. This tour of macros is followed by a case study introducing a Forth implemented in Lisp using the lessons learned earlier.
And why did I find it tough?
The problem was not the wealth of information presented but the way it was presented: the author is a Common Lisp zealot and keeps on preaching its superiority. I find that hard to take.