I downloaded this series about two months ago. It is overwhelming to listen to almost 2 years of teaching in 2 months. John Piper does an exceptional job in Hebrews (as elsewhere).
The teaching is different than a word-by-word study. Piper takes the text in sections and draws out the overall teaching. It it not a series to answer every question you have about the book of Hebrews, through he does answer many (especially the hard ones). Instead, Piper acts as a pastor desiring to take his church through Hebrews, highlight the driving force of the book and encourage his congregation to read and study the book too.
The best parts, or the ones I remember most vividly, are chapter 6 (the difficult section), chapter 10′s section on the church and small groups, chapter 12′s discipline by God and chapter 13′s need to go outside the camp.
I would encourage you to listen to this series to take a mature look at some of the great themes of Scripture.