This is the second time, I stayed at this hotel. Centro Hotel Stern has two properties: the original Hotel Stern, and the new Centro Boutique 005.
During both stays, the staff was friendly, and the breakfast superb for my taste. Both times we stayed in the Centro Hotel Stern house.
The first time, I had a single room with a little balcony which was clean and alright for the price.
The second time, we had a family room. The beds were alright and clean. The carpet desperately needed a cleaning. The toilet (separate from the sinks and shower) had a weird smell when the ventilation wasn't running. The windows were noise insulated, but we had to keep them open because of the heat. There happened to be an overnight road construction at the nearby intersection. The shutters were either missing or broken, and the curtains not light blocking, so there was a constant room illumination from the street lights. We survived the two nights, but it wasn't a good night sleep.
That said, I booked now in the new Boutique 005 house, because I really like the breakfast (and the restaurant has tasty German food for lunch and dinner).