This book is small and easy to read. I think it could be a good starting point for people who are starting to read self-help books. It mentions many concepts from other authors and could serve as an introduction.
For others, the book lacks depth, research, or practical advice. There is just not that much to it. I agree with what it is selling, and I wish it did a better job at doing it. Kudos go to popularising the Ikigai concept. I believe it's a good alternative to be mindful of in Western culture.