Writing: The writing is quite easy even though it´s a dense book! It usually felt like a friend was telling you about his project and the results he found.
Credibility / Research: Well, obviously there is already everything found and said about habits, psychology and philosophy. With that said, if you studied this topic to the very end you probably wouldn´t find anything new in here. And that´s okay! Where this book shines is the fact how good everything is summarized and explained. Because there is so much information you have to find a way to give your text structure, read-ability and logic. I think that this book is the ultimate summary of everything "habits".
Personal impact: The quote states that expectations determine our satisfaction which is so true if you read some of the reviews on this book. "Well wasn´t life-changing." Of course it wasn´t! You read ink on paper, how can this be life-changing? I get where people come from but they suffer from high expectations. This isn´t a theoratical advice book, this is a practical adivce book. I think that if a human would live a way like described, it can be really benefical.
Problematics: The rich, white man privelege... If you read some of the pages to a poor, black woman in a developing country and say "Well it´s your fault how you live. If you really want to change you can." would be extremely harmful. That might was a bit extreme and stereotypical but same goes for addicted people or people with eating disorders. Promoting diet culture like in this book can be harmful, physically but most important mentally. So yeah, this book is advertised to an already privileged group but a little disclaimer at the beginning would be nice.
Conclusion: Honestly, the problematics relate to almost every self help book, so letting this one book suffer from criticsm wouldn´t be fair. The positives really speak for themselves. It´s a five stars for me. If you want to criticize this book based on being poblematic, please speak for the whole self help genre.