Movie sequels

Shrek the Third, Spider Man 3, Die Hard 4, Bourne Ultimatum. Hollywood doesn't seem to be willing to risk it and has been making more movie sequels than ever. Jeannette Catsoulis analyzes the phenomenon in this article published in the New York Times. What do you think? Can sequels be as good as the first film of a series? What are the ingredients of a good 'movie 2'?