Overrated. I honestly don't understand why this book is so popular. You can get everything you need by reading "A Christmas Carol" by Dickens, any of Sylvia Plath's works, and the actual philosophy works superficially mentioned (Bertrand Russell, Henry David Thoreau, Aristotle, and Albert Camus mainly). I haven't seen it, but I gather watching "It's a wonderful life" would also have the same effect.

The obvious stuff: the story was too long, and the structure was incredibly repetitive. I was frequently bored. It was frustrating that the main character (Nora) had no functional knowledge of each life she was 'trying out' so was painfully clueless a lot of the time. Unfortunately I read this as an audiobook. If I had read it as a physical book, I would have skim read/skipped the vast majority of the middle and end sections. I'm definitely not an expert, but the diction and syntax also felt poor to me. Again, oversimplified and repetitive to the point of frustration.

The less obvious stuff: The author's attempt to incorporate different schools of philosophy, psychology, and physics again borders dangerously on the harmfully superficial. I applaud the effort to try and make these topics (existentialism, multiverse theory, Gestalt theory) accessible to a wider audience. But the oversimplification and lack of exploration of each topic doesn't do any of them justice. Plus, to those of us that have read these sibjects, the book's narrative sometimes contradicts itself when using them which is just disappointing. 

Bottom line, I don't believe that we ever actually get a clear, consistent, message in what the book is trying to say about the nature of the purpose of life or regret. 

I get the feeling that the author wanted to investigate these themes and make it accessible, but got too tangled up in themselves to make anything coherent, and unfortunately as a result, also enjoyable. I give this a generous 2 stars for the attempt, because judging by other reviews, clearly some people are benefitting from it.