The main novelty here is that the author just made the entire book available to the public for free.

I have previously read the printed version, so maybe now is a time for a very brief review. The book is technically fascinating and a worthwhile read, but it is also highly opinionated even by Lisp standards. Then again, it is refreshing in this time and age to see this deeply human and creative side of programming. I wholeheartedly recommend others to read it - and to carefully choose which of the advice to follow and which not :)

Thank you so much, Doug Hoyte, for making this book available to all of us!

Looks like the well known book has just become free (online or PDF)

The book is wonderful to read and get your mind blown by all the ingenious, clever, and surprising things that are possible using basic building blocks of Common Lisp - so that you know exactly what code you should NOT be writing when doing Lisp for anything serious and involving other programmers.

It's very good for realizing the difference between what is possible and what is feasible, since Lisp mastery requires both knowledge of what is possible to do and restraint in the actual use of those possibilities. Clever things require cleverer debugging techniques, and Let Over Lambda is absolutely full of the former.