Doesn't say anything I haven't heard before.
James Clear needs to specify more clearly why we should listen to him... what are his actual qualifications? I'd much prefer to read a book by multiple psychologists and psychiatrists rather than from one seemingly random guy.
James Clear doesn't talk about Neurodiversity and mental health in its relationships to results. For example, if I get depressed, then I may become bedbound and not be able to carry out my habits.
Another example, is if I have ADHD then it will on average be harder for me to do habits and the way habits will be done for ADHD folk will tend to be different than for neurotypicals.
He talks about systems but that's just what I did anyway, I studied 4 hours a day at Uni and then graduated with a 1st class honours.
Also I already had the habit of doing exercise at least 3x per week because I know how good it is for my mental and physical health.
Habit change strategy that I can recommend is a written and signed contract: I was biting my nails so I created a written and signed contract between myself and my ex girlfriend that if she sees that I have bitten my nails, I have to take her out to a luxury restaurant spending at least £100 on the meal. After making this contract I never bit my nails again whilst I was with her.