The staff was rude, the room was small and far too hot and there is no air-conditioning control in the room. Also the breakfast is charged 25e, which is more expensive than in the best restaurants in town, but the selection is very poor (scrambled and boiled eggs, a few types of charcouterie and cereals, and basically that's it). Additionally, I have noticed that there is no food for people with dietary restrictions (sugar free, gluten free or similar), which is a standard in most hotels. An absolute rip off! How this hotel is ranked as a 4-star is beyond me!
If you are coming to Otto-Hann Ring you probably have a meeting at Siemens or RR, you are far better off staying in an a other hotel closer to the city and taking U-Bahn to the meeting.