Spent 3 nights recently at the Artotel Berlin Mitte.
It was supposed to be a designer hotel, I have searched for the design, but I haven't found any kind of design in the rooms. May be the restaurant have something, but the rooms are poorly decorated, with common furniture. The bed was not very comfortable. In the bathroom there is only liquid soap with two small towels.
Do not expect any kind of luxury at Artotel Berlin Mitte, it is only a basic hotel, but with a convenient location (50 meters from the metro, 2 metro stations from Alexander platz).

The breakfast was good and the staff friendly.

Directly across the street from an informal bus terminus the hotel is also very convenient for the U-Bahn into town and some points in the East on foot, but quite a walk away from the heart of things.

The staff was friendly and tried to be accomodating, but couldn't give me a non-smoking room for the first night, nor an internal room, and I was woken by the early morning firing up of the local bus service (a courtyard-facing room is essential unless you have industrial strength earplugs.)

The rooms are small and ill-conceived. Too much attention on 'fabulousness' throughout the hotel (the public spaces are sleek and unwelcoming) and not enough on basic guest comfort.

Our first trip to Berlin, so we were unfamiliar with the city layout.
But we were drawn to the design of the Art'otel. Yes, the public spaces are nicely designed, as are the rooms. But the rooms are small and not very functional. And the location is definitely out of the way (although there is an U-bahn station just a half block away). And we were really put off by the tourist buses and groups. Not really our scene. If you do end up here, be sure to specify a room at the back of the hotel. The ones on the front are very noisy.

We spent two nights in the Art'Otel Ermelerhaus in April 2003. The design of the place is great, but whilst the common areas were spotless, the room had definitely seen some wear and tear. The walls looked like the hadn't been painted for a few years, and the shower wasn't working properly. Also not the cleanest room I have seen. On a more positive note, the breakfast was sublime and the breakfast room had a lovely atmosphere. All in all not a bad place to stay, and the price was very reasonable at EUR 115 per night for a double with breakfast.