The apartment is located excellently in Kreuzberg were close to a lot of excellent bars and restaurants. Also within walking distance from Potsdamer Platz and several museums and parks. 10 out of 10 for location :-)
The apartment was super clean, but it doesn't look exactly as it does on the pictures. It is a little gloomy, since it is sort of stuffed away in a narrow back courtyard. Also some of the furniture (the table, for instance) isn't as nice as it is on the pictures, but as a whole it is a good apartment.
Also, beware that there is two streets in Berlin with the same name - be sure to set your GPS to the one in Kreuzberg :-)