There is a wide range of issues discussed, the successful interventions for depression, about "Grit" (a positive, non-cognitive trait) through to critical treatment by precisely those with antidepressants compared to placebo therapy - there's plenty to learn Flourish in.
What I personally find not so good: the book has lengths. Mostly it shows Marty Seligman to his science-oriented style. And although there are amusing passages, had at least I personally also a good deal of "Grit" needed to stay tuned.
The book and its importance for the research direction is undeniably there and therefore it remains in my opinion, for a long time, a must-have for those interested of Positive Psychology.