Looking for restaurant with German cuisine and Berlin atmosphere

My favorite restaurant of that type is the Joseph-Roth-Diele, Potsdamer Straße, named after the well known writer ("Radetskymarsch", "Die Kapuzinergruft").

No specific recommendations, but it may depend on what you are calling "German Cuisine". Most dishes Americans think of are actually specific to Bavaria, a good comparison would be thinking of American food, but meaning Southern Cooking.

In Berlin, I recall finer dining German restaurants serving local cuisine, but fewer Bavarian style dishes. There are restaurants that serve mostly Bavarian food though if that is what you want, they tend to be more casual or Beer Hall atmosphere.

@sla019: the lunch menu of the week does not look very much like German kitchen. Rest of menu looks little better.

@OP: You will have a lot of options, e.g.
+ Zur letzten Instanz (one of Berlin's oldest)
+ Borchardt
+ Dicke Wirtin
+ Tiergartenquelle
+ Bötzow Privat
+ Dicker Engel
+ Wendel
+ Speisehaus Berlin
+ Joe's Wirtshaus
+ Wirtshaus zum Alten Fritz
...

@sla019: the lunch menu of the week does not look very much like German kitchen. Rest of menu looks little better.

Hm .. is there a "German kitchen" at all? Anyway, what I should have said is that the Joseph-Roth-Diele was originally recommended to my by Berliners as a typical and untouristy Berliner Kneipe and that I like to have my lunch with them there every time I have to do in the Staatsbibliothek. I was neither claiming that it is the most typical local restaurant nor that I do generally expect "good kitchen" in that type of Berlin restaurants ;)

For Swabian food (specific sub-type of German food) in a Kreuzberg atmosphere (specific sub-type of Berlin atmosphere) on the cheap, go to Spätzle Express. Get a small -- it's plenty of food and comes with a salad.

http://www.spaetzleexpress.de/en/food-menu/

On Thursday evenings on Eisenbahnstrasse in Kreuzberg Markthalle Neun has "Streetfood Thursdays" where you can find vendors from Asia, Africa, the Middle East, and Latin America as well as loads of locals. So many foods its tough to list them all but there's definitely something for everyone. I had malthashen (German ravioli) a dish I hadn't eaten since my grandmother passed away in the 1980s and my wife found a vendor that had an olive quiche. I recall whole roast pork BBQ, grilled cheese sandwiches with sliced apples, gelato, etc. Now this might not sound like the "Berlin atmosphere" you were asking for in your post but the hall was full of thirty-something Berliners so from this perspective it might fit the bill.