I don't think people realise that Motel One is not actually a "hotel", that is to say, they're so good at what they do that people don't realise that this is NOT a hotel. There's a bar that's open late, and there are always a few people hanging around. The bar-keep, as well as the night-manager, are both friendly, helpful, and available at all times. If you're sleepless (like I was), it's not because the room's uncomfortable in any way, but because the neighbourhood of Hauptbahnhof is filled with beautiful cobbled streets, and sometimes you can see the bar-keeps cleaning up the bars that you can tell have been there for decades. The rooms are perfectly minimalist and designed so efficiently that, as a student of architecture, I ended up gushing praises to the receptionist at checkout when she asked me how my stay was. And they keep it so clean in that well-organised room that I actually asked the friend I was sharing a room with if he was deliberately keeping the bathroom clean because of my obsessive-compulsive cleaning habits, and he said he wasn't, so I guess it's just the cleaning-staff doing an excellent job of keeping things organised and in order, and we were never the wiser.
Fun tips: There is no room service, but there's a grocery-store across the street where they sell wine, and the bar is happy to provide the appropriate glassware to enjoy drinks in your room. The bar is open all night, anyway. And the breakfast, for around 9 euros, is so German and so lovely that we ended up inviting team-members not staying at Motel One to try it (they loved it), as well as making friends with members of the staff during the meal over the course of the week, because the food is just that good, and they're just that pleasant, friendly and helpful.