My son and I stayed at Hotel Carmer 16 for 4 nights in July, 2010, as part of a 3-week vacation in Europe celebrating his high school graduation. This hotel was one of the best places we stayed during that 3 weeks. The rooms were large, well-furnished and comfortable. Ours looked out onto Carmerstrasse, which was nice in itself. The neighborhood is quiet and pleasant, but with easy access to the Zoo/Tiergarten U-bahn, S-bahn and bus station, so all of Berlin was easily and quickly accessible to us.
The staff couldn't have been more helpful. We found them knowledgeable and interesting as people as well. Everyone was highly fluent in English, very helpful since my German is what I remember from 4 years in high school 35 years ago. The staff loaded us up with information, maps, brochures, and when needed could sell us transit cards, making it easy to use Berlin's excellent public transit.
A special word about breakfast: it's great. Smoked salmon on rolls, fresh fruit and vegetables, but American eggs and bacon too for those who need them. Several mornings I took my pot of coffee out to the sidewalk while my son slept late, and sipped there as the world passed by.
The hotel is not air conditioned. It was hot while we were there. We received fans when we checked in, and used them in the room. The heat was the only drawback of our stay.