Like most of the Piper books I read, it's a bit slow going because of the content-however I am always blessed and convicted by reading it and can't wait to read another :)
So, as I said in an earlier post, I highly encourage you to read this one.
I was especially blessed this mornings chapter, Finding God in the Garden of Pain; here is a quote from John Chrysostom:
Fasting is, as much as lies in us, an imitation of the angels, a contemning of things present, a school of prayer, a nourishment of the soul, a bridle of the mouth, an abatement of concuspiscence; it mollifies rage, it appeases anger, it calms the tempests of nature, it excites reason, it clears the mind, it dis-burdens the flesh, it chases away the night-pollutions, it frees from headache. By fasting, a man gets composed behavior, free utterance of his tongue, right apprehensions of his mind.