I always found "Lisp in small pieces" extremely heavy to read. It's not the content per se but I find the writing style baroque to say the least . I attempted to read it twice and never went further than the 2nd chapter. Am I the only one?

Instead I found PAIP the best introduction to Lisp for somebody that has already (plenty of ) experience with other languages. The introduction to the language is concise and smooth. I liked much only the chapters on the language though. The chapters on AI are too much outdated for me to find them entertaining even if the Lisp code is pedagogical for sure.

I didn't like OnLisp at all: the book wastes too much words on saying how much Lisp is great and the best thing in the universe rather than going straight to the point. I don't like this kind of style at all.

I found Practical Common Lisp too slow for my taste and would reccomend it only to a beginner.

For me the quickest way to learn Lisp for an experienced sw engineer is to start with PAIP reading only the first 4 chapters about the language and then to jump straight to a good reference guide such as "Common Lisp the Language, 2nd Edition"

Also I suggest anybody that is interested in CL to have at least a look at Julia. Since the relese of Revise.jl the interactivity of the REPL is second only to Smalltalk and CL but multithreading support is consistent amongst all platforms and the library ecosystem is already interesting. The language has a lot of momentum, is rapidly evolving and the community is small but helpful.