We have been miserably failing at the Penguin Classics challenge. In fact, I have only read one (and it was super thin), before I was distracted by Bill Bryson's At Home, which I stole off my mother promptly after giving it to her for Christmas.
Anyway, the one I have read was not strictly a Penguin Classic, but from the Penguin Great Ideas series, but that's just the non-fiction equivalent, so still counts. It was Books v. Cigarettes by George Orwell. I have very much enjoyed it, partly because he is a good writer, and partly because he really hates totalitarianism, which I am also not a fan of.
The first half is a collection of short essays, containing his musings on working in a second hand book shop, why people don't read as much as they drink/ smoke (not due to the price of books, says he), why freedom of speech is awesome (and totalitarianism is not), why one should avoid ending up in a public hospital and so on. He comes across very learned, and has excellent turns of phrase, as well as a good appreciation of liberty, although this was tempered with an oddly fervent patriotism for someone who seems to be generally skeptical of the state, though I guess it makes some sense in the context of Britain being at war with real totalitarians.
The second half I enjoyed only slightly less. Over several short chapters in tells of his years growing up in boarding school, which were largely miserable. He has some very interesting insights into the way he thought and learned as a child, which I liked, but I guess the subject matter was just not as appealing to me as that in the first half.
Overall I wished there was more of this very short book, and came away thinking even more highly of Orwell having read his actual essays than I had based on his parables.