Penguin's Great Ideas series

Just over a year ago, the Bookseller announced the third and final series of Penguin Great Ideas. According to Adam Freudenheim of Penguin Classics, "Sixty [three batches of 20] feels like a lot of great ideas, and if you went beyond that, you would begin to be scraping the barrel." But here we are, a year on, with yet more Great Ideas coming out and plans in hand for a fifth series; and, it has to be said, there is little sense of any barrels having been scraped.