tl;dr I personally found this to be a worthwhile read. Definitely do the work and questions the author gives out and really take your time with it. I got a lot out of this book, super glad I read it. :)
Not tl;dr
It took me some time to go through this, not just because it's in Japanese and I read much slower in Japanese, but also because I wanted to let the concepts sink in and do the actual work discussed, since I am in a spot where I don't have much direction in life.
I saw reviews that this book didn't seem to bring anything new to the table, was just so-so, and perhaps because I haven't dug into this genre, I have a different perspective, but for me, I didn't find that to be the case. I've read (English/Western) articles on this topic before, but something about how it was worded here hit me differently. Maybe it was because I was going much slower, that I gave things more thought, but I personally found it very worthwhile to have read.
That said, this book seems aimed at post-grads or those in their 20s. So I'm a little outside the demographic, haha. Some of the career examples were quite 'young', and YouTuber was frequently mentioned. Certainly a job field you could go in, but speaking from personal experience, not one to quit your day-job over. Regardless, the advice still held up for me, despite me being a bit older. Aside from the few career examples, really this book could apply to any age group. (No doubt people in their 50s or 60s are still wondering what to do in their life! And this book isn't just applicable to careers, it could work with charities or volunteer work too!)
The author discusses three main factors in determining what you really want to do: what you like, what your (soft) skills are, and what is important to you in life. At face value, those concepts don't seem that deep, but the author explains it's much more than what's on the surface, and really has you look inward. (Definitely do the assignments given! And take your time with them!)
While I didn't ultimately reach a conclusion on what job I really want to do, I wouldn't say this book was unsuccessful by any means. I got a more concrete idea of what I care about, what I want in life, and ideas of directions to go that I didn't have before. It's a lot to think about, and I appreciated how realistic the author was with everything. That not every job is permanent, so knowing who you are and what you want will let you be flexible enough to change with the times and your passions.
And I appreciated that even the author mentioned some directionless after finding out what they wanted to do. That they had to sit with it for a while, digest, and also naturally start to come across more/new information and options, since they began to recognize what to look for.
That said, you can grab the freebie bonuses at the end of the book for additional questions to answer, information, and assistance (baring you have/make a Line account, which I did just for this, haha).
The biggest negative for me with this book was not a fault of the book per-say, but Kindle. The images were often so small as to be unreadable, and I couldn't zoom in. So that was frustrating. Luckily the information is all already there in the text, but still, sucked to miss out on the visuals.
All-in-all, for me personally, I really enjoyed reading this book. Definitely discussed it a lot with those around me, and everyone seemed to enjoy the concepts and conversations it brought up. :)
For Japanese Learners: This book was a solid N3. There was a lot of repetition, things reworded differently, and approachable grammar, making this a nice book to practice with and push yourself. A good challenge for N3, something more relaxing for N2.