Let me start out by giving you a little piece of context. I have been following Nir's work for the past two years, and for the better part of that time I have been helping him managing his now massively popular blog. I have also attended multiple of his talks, and have even given a talk on the topic myself this previous summer.
It is safe to say I have a better understanding of the topic than most, yet Hooked managed to provide me with even more insights and was a really enjoyable read from beginning to end.
In short, Hooked is a handbook for designing habit forming products, and Nir explains his four step framework (consisting of trigger, action, variable reward and investment) patiently and thoroughly. At the same time he backs up all his claims using a plethora of solid academic research, leaving you confident that he really knows what he is talking about.
After explaining the framework, he also discuss how product designers can use this newfound super power for good (yes, it really is a super power), rather than callously exploiting their users. He also provides the reader with practical steps to implement his teachings in his/her own work throughout the book, and ties it all together neatly in the last chapter.
Overall an excellent book that I highly recommend to anyone interested in user psychology, engagement or product design. Even if you're just curious to learn more about how products create habits and shape our modern lives you will find Hooked highly valuable.
PS! Until Dec 31st you can download a free Kindle version of the book, so get it now!