This could be described as a budget hotel, it cost about £55 a night (For a double), and this was over the busy xmas market weekends. It could also be described as a business hotel. I'll describe it as an excellent value for money hotel.
It's not the place you take someone to impress them, but it was clean comfy, the staff helpfull, the inclusive breakfast excellent, and the location convenient. The rooms aren't huge but they're not small, there are no tea or coffee making facilities in the room, but if you know this in advance then take a travel kettle like we did, or pay the businessmans upgrade, which costs E15 for tea and coffee facilities, a small bottle of wine and a few other extras which I can't remember. It had a very nice bath in the room, the bed was very comfy, pillows were thin, but I asked for extra and it was no problem, staff were also friendly.
I stayed in the marriott in the media harbour in the summer and it was £90 a night with no breakfast (£127 with breakfast for double), whilst it was a cut above the mittel, it wasn't worth anywhere near double if you include the breakfast.
Also and this isn't mentioned on Roomex, every person also recieves a card which gives you free public transport within dusseldorf and its outskirts, this includes the S7 train back to dusseldorf airport, from the HBF (main staion) which is about 7 minutes walk from The Mittel. Other nice things included, letting us put our bags in our room at 11am ( check in 2pm officially0, we were told the room hadn't been cleaned yet but we could put our bags in if we wanted nice touch. also leaving bags at hotel at the end of the stay was fine too. Bar in lobby is also very reasonably priced.
Overall, great value for money, and checkout was easy, gave them the Roomex email at check in, no imprint of CC needed and checkout was a formality. Very pleased, if you want a reasonably priced clean and comfortable room, The mittel hits the spot.