Radical Acceptance packs a really powerful punch for those who find it at the right time in their lives.
The subtitle for RA is "Embracing your life with the heart of a Buddha."
This is a book on mindfulness, meditation, and spirituality for those who are into that sort of thing. Like I mentioned I think for anyone who is struggling to find happiness or seems to be bogged down by troubles and sees no escape, Radical Acceptance as a book and as a philosophy can be extremely helpful.
Each chapter in the book addresses a different area in your life that you may be struggling to accept and provides guidance on how to deal with it. Tara is a psychotherapist in addition to being a teacher of Buddhist meditation and so the book is full of stories of Radical Acceptance being applied in tough situations, which might seem like radically anecdotal evidence (pardon the pun), but can be very helpful considering that the whole point is you've got to accept things and let go. There are also plenty of guided meditations included to help you deal with particular situations, which may make this an even better book in audio format.
I find a very close connection between the thesis of Radical Acceptance with the Latin amor fati - "a love of fate" which was embodied in Stoic philosophy.
If you're not quite ready to dive headfirst into something quite so mystical sounding, 10% Happier is a great place to start exploring mindfulness and meditation. Dan Harris actually comically makes mention of Tara Brach in the book several times as he encounters her at mindfulness seminars and warms up to her ultra-serene personality as he spends more time around her.