The historical perspective is very enlightening, in particular as regards the situation prior to Vatican II, which warranted Pope John XXIII's call to the bishops, and Pope Paul VI's continuation of that mission. The enormous scope of the project is revelatory. So often, in perplexity about developments since Vatican II, the times before the council can seem either halcyonic or anachronistic, perhaps especially for those who hadn't yet been born.
Ratzinger, writing as a young, already brilliant scholar, lays the cards, the reasons, on the table clearly and fairly, as one who was there. His writing even then was extraordinary. The perspective this brings to later, sometimes troubling developments in our Church is valuable. If you have current concern for, and hope in, the Catholic Church in our day, this text is worth the price and your time.