GoF --> -1 Overrated. Not because of the book, but because of most of the idiots who didn't conceptually understand the applications after reading. Half the people who try to talk in patterns don't understand the difference between Command, Visitor, Chain of Responsibility, etc. They understand Singleton, and that's it. Of the people who can talk in patterns, a good 50% don't really know how to appropriately use them together in system and software architecture. Meaning, at best, 1 in 4 of those who reference GoF patterns are actually using the work to help in communication and design.
I think it's probably an important book in the history of Software Engineering (not to be confused with CS). The book unfortunately spawned at much bad design as it did elegance.