The room was quite small but especially the beds, and certainly the duvets are really thin and simply too small if you're very tall. In germany I've mostly encountered super-awesome duvets so this was definitly a downer. 5€ per day for the wifi sucks of course. I once handed over some laundry to be done and while service was very good, it wasn't so clear to me that this costs about 50€. The Sauna area at the Steinberger Sonne, while very good, never had any staff at it's desk (I only went between 7 and 10 pm though). It is cosy and well-equipped though I must mention the quite loudly ticking clock which was stuck at 3pm or something - this was the case the full 2 weeks that I used the sauna.
The breakfast is exceptional. It has literally everything you want - except freshly squeezed orange juice, but in all honesty, I don't know any hotel who makes freshly squeezed orange juice. The breakfast most notably features mini croissants every day and alternatingly features mini donuts and mini boule de berlins. Clean bathroom. The wifi is also very fast, but at 5€ a day or 30€ a week, at least that is to be expected. The hotel is the little brother hotel of the big Steigenberger Sonne hotel some max 50 meters away, which has an excellent sauna that also guests of the Kleine Sonne can use, which is great.