kurzer...! 
What's your interests when visiting a city of that size?
The mayor of Berlin - a very incompetent and arrogant man, btw. - says Berlin is "poor, but sexy". I am not convinced that it is that sexy, but I am damn sure that it is poor.
If you use public transportation, try to avoid the "S-Bahn". Too many problems with that, it is impossible to make a statement on whether or not it will work reliably the day you use it. It is a disaster story since several years now. Could as well let you wait three hours for the next train. Subway worked fine last time I was there, it was always my preferred transportation method. But better do not travel by subway ("U-Bahn") alone in the night. Assaults take place quite frequently now.
Prepare for some extraordinary unfriendliness if you happen to run into a Berliner
original. "
Kodderschnauze" is part of the old Berliner's way of life.
Where else do you go in Germany? The "Spreewald" is not far away, if it is countryside you look foor, that might be a good target mark.
http://en.wikipedia.org/wiki/Spreewald If you crisscross the country, as usual I recommend the old town of Lübeck, also that of Wismar close by. Both towns belonged to the famous Hanse alliance and you see it in architecture: Wismar looks like a smaller copy of Lübeck.