Just purchased the new Osprey on the Spanish Tercio. Highly recommend it - features illustrations by Gerry Embleton (one of my favorite Osprey illustrators - particularly of 15th and 16th century subjects). Its an overview of the period (albeit for one unit type), covering almost a century, so it lacks the in-depth detail of something like their book on troop types during the Armada campaign, but still well worth the money. (If only they would do a book on the Eighty Years War!)