The single person room was okay and I got a tea kettle and some instant coffee (I emailed the staff in advance). 24h reception service was handy.
The elevator was weird, when you stepped in to the elevator went up an inch and came back down before the doors even closed.
The air quality in the room and in some of the hallways was poor, but opening the windows helped. The room got hot during the nights too.
The shower section of the bathroom had cracks in the doors/walls. The water always leaked to this corner on the floor (doors where shut).
No noise complaints, my room was located in the end of a long hallway on the 2nd floor. It had a window sill and thick walls.
The staff was ok, but not the best/friendliest service I have seen. They ordered a taxi for me, so that was nice. Check in had some problems, checking out was easy and fast.
Not the comfiest stay, but I would still recommend, because the area seemed relatively safe and the metro station was just 3mins away. The staff told me that Tegel airport would be a 30min drive away (at 4am), but it was more like 20mins with no traffic.