I don't recommend it unless you are familiar with it, and accustomed to moving quickly as a traveler, but 3 hours at ZRH is approaching the amount of time where it would be entirely possible to sneak into town and enjoy a quick bite and/or bier.

The easy accessibility of ZRH from the city center is one of its many great advantages. Certainly not the same with MUC or FRA.

I too am very partial to MUC, one of my favorite cities and airports in the world. If the Airbrau is open, I can't think of many more enjoyable places to spend an airport layover.