I'm a big fan of Hogarth, and this book, like his other instructional drawing books, is superb, covering anatomy, ageing and wrinkles, different types of heads including different racial features, and hundreds of great reference drawings of full heads and individual features. If you're looking for a more general book, "Dynamic Figure Drawing" is far better, but if you want to go into detail with heads and features this is a good purchase.
My only disappointment with it was that, though it covered everything else about the face in detail, it did not cover facial expressions, despite dancing around the subject. I'll probably look for another book on that subject, but it seems a strange omission to me as it would be a natural extension of the discussion of the facial muscle system, and I would very much have liked to see Hogarth cover it.