We were on 4 day trip to Berlin this month and happened to drop into Burgermeister three times during our stay. I'll be honest, I'm not a massive burger and fries kinda guy but I really enjoyed every time we ate here.
The outlet itself is situated underneath a train overpass in East Berlin, and is always packed, especially late at night. Their burgers are delicious and their fries are some of the best I've tasted. Expect a young, hip, bohemian crowd hanging out here at night. They also have a good selection of beers and its relatively cheap. One downside is they could do with a few more seats.