This book is a great exposition of metaphors in the Book of Psalms. He carefully explores the core imagery and links together related imagery in a way that helps one see the full arch of the book. Though it sometimes bogs down with unnecessarily difficult vocabulary, the book definitely helps one encounter the psalms with fresh eyes and heart.
My only major criticism is that his exploration of Psalm 139 was incomplete and disappointing. He only dealt with the verses that are comforting and not the challenging lament verses. As such, his closing chapter, which ideally should drive the whole text to a nice conclusion, is lacking.