My edition is actually called "The Heidelberg Catechism for Today", but I'm pretty sure it's the same book, although possibly a different translation. The book itself is simply a collection of two different sets of lecture notes based on lectures Barth gave on the Heidelberg catechism. The first is more expository, the second is more topical. I was surprised how in both he did not talk a whole lot about the whole law/gratitude sections. I'm starting to wonder if that's typical of Barth. He seems more interested in metaphysics than ethics, I guess you could say, perhaps.
Anyway, this book is very interesting from a perspective of trying to understand Barth better. It's not, however, necessarily the best way to learn about the Heidelberg Catechism. In this way, it's similar to "Dogmatics in Outline" which is similarly taken from Barth's lectures on the Apostle's Creed. Their both interesting books, and there's definitely valuable stuff in them, but at the same time I can see why neither are best sellers. Books like these based on lecture notes don't usually make for the best reading. It is an interesting way to see some of the peculiar and/or interesting way Barth looked at theology, though.