Zimmer has had several years to get it together yet he still has the same "bend-but-don't-break" mentallity he has always had, which is based on the "fear of getting beat". Anything based on fear is doomed to failure.
I don't like Zimmer's style because I want a defense that will create turnovers, score defensive TDs, pressure the QB, and dictate to the other team what they can do. Zimmer's philosophy is to try to limit what the offense wants to do (that's what he has stated many times). "Dictating" and "limiting" are two very different styles.
Good QBs will always find a way to beat this defense because they have too much time. No matter how good a DB is he can't cover indefinitely and eventually the QB will find him if he has enough time.