So far I love this book. It has clear useful information on design. Things like a formula for doing ovals. He says clear things like (paraphrase) if you increase on every round of a circle you will eventually begin to bunch up so crochet a row without increasing to fix this, and if you increase in the same location the edges of your circle will begin to flatten out so move your increases around.
As the book progresses it gets more creative, but I've only skimmed those pages. He goes through freeform crochet, crocheting with your fingers, spirals and other things. He also has stitch patterns which I haven't gone over yet. The book is from 79, so not many color pictures. But I haven't seen any recent crochet books that go through quite the same material. Unfortunately its due back at the library, and it won't let me renew urgh. I think it may be worth $60, depending on what your goals are. I rented my copy through a university library system.