I know Munich okay, as my wife is Bavarian (well Franconian really). I've been there maybe half a dozen times. Unfortunately never for more than an afternoon, so I don't really know the nightlife.
Our usual beer-hall experience is the Augustiner restaurant on Neuhauserstraße (not to be confused with the Augustiner Keller beer garden). It is lively and fun and not so touristy.
For something to do, wander around the Viktualienmarkt in Altstadt. Founded in 1807 as a small 'herb market', Viktualienmarkt has developed over the years into one of Munich's biggest markets with an amazing array of meats, cheeses, fresh flowers, fruit, vegetables, and fish.
The English Gardens are very nice, but in the winter they are usually quite dead on account of the weather.
The city of Munich has a really good interactive website where you can pick a neighborhood and then see pictures of many of the restaurants, bars, etc there - it is partially in English. Go to