"Four Thousand Weeks" is a weird mix of productivity and stoicism advice. It reiterates many main ideas from the books on the topics and tries to bring something new to the table. The primary recommendation of the author? We are mortal, so start enjoying life now, not sometime in the future.
Oliver masterfully mentions that when you become more productive, you don't get more free time — you start doing more. This never-ending race is why most productivity systems fail and lead to burnout. When you are constantly moving the goal forward, you never reach it. One might say that the author is nihilistic.
Unfortunately, it is far too easy to take this advice literally and start believing in that tale about a fisherman and a businessman. "Why don't you fish more, get more money, hire more people — but then do the same, yada yada yada." You know what? Screw everyone that brings this story up. The fisherman is alright until the government raises taxes, one of his family members experiences a medical emergency, or there is no more fish in the ocean for some reason. This story is remarkable and all but highly unrealistic. I bring this up in my book.
However, the author does have a few great pieces of advice — even though it is so profoundly hidden among the rest of the existential horror that you would probably miss it. Some of the good parts are similar to what I suggest in my article on being more productive.
Overall, skip reading the book. The topic is "Yeah, you can try to be more productive, but why bother?" It would help if you were bothered, though. But simultaneously, you must realize that the best time of your life is now. Make time for both productivity and leisure. Make time for your family and hobbies. Find the compromise, don't jump from one extreme to another.