I am not too familiar with this type of books, namely, "devotionals". I think it was Martyn Lloyd-Jones who said, "I do not want someone else to do the devotional (meditation on the Word) for me" and warned about relying on someone else's meditation and neglecting to do his own.
However, that does not mean that this type of books is useless altogether, I don't think. This particular book, "Pierced by the Word" contains a collection of thoughts and meditations from one of the best preachers in the world, and it shows that. The chapters contained in the book isn't always a direct meditation on a particular passage from the Bible, and some may say that is not a good model to be given in a devotional book. I agree with that. But the book as a whole and each individual chapter gives a great encouragement for the reader to live more faithfully, courageously, and passionately for God; it certainly did for me.
The challenge it gives is Piper classic. Biblically and theologically sound trail of thoughts does not simply die in the theological arena, nor it is buried in the pages of the Bible. Piper always shows, in each chapter of the book, practical ways to reform our minds and outward actions into more faithful and God-honouring ways.
This book has 31 short chapters, and it can be used for a month to help you deepen your understanding of the over-arching theme of the Bible and Christian living by reading one chapter a day. Each chapter also ends with a short prayer that you may choose to make it your own. I think you would still want to do your own devotion, QT, meditation, whatever it's called with the Bible passages yourself while you are reading this book, but over all, I highly recommend this book for those who want to give a month hearing a godly brother and learn from him.
(This review is also posted over at Shelfari for those interested.)