Comfort room is very small and not cheap.
Asked for a queen bed, got a single bed.
Try not to get a room facing the street, too much traffic noise.
No way to adjust the temperature in the room.
No free transport card like other hotels in Germany.
Expensive Internet.

Will not go back.

I'm staying every year few days in Dusseldorf and last 5-6 year my choice is Nikko. It's very well located, rooms are nice (I even think they renovated some of them), service is fine and spa is also very good. Japanese restaurant is also ok, but prices are too high. You have several Jap. restaurants around (one just right of the hotel entrance and it's GREAT) so no need to eat here.
The only think that I don't like is that you have to pay extra for everything: spa, internet, breakfast.... This year they offered me upgrade to better room and free wifi for 15 € more, so that was a good deal, but hotel this class should have wifi for free and also spa for free.

My one night stay for business purposes was very nice. The executive room was big, newly renovated, the bath without tub but with a great shower was very nice. Breakfast was good although service was difficult to get hold of. All in all, nice hotel.

I went to the hotel expecting a large business type hotel which is really what it is. However, the rooms are very well appointed with coffee makers (lavazza excellent), mini bar, etc. We had an executive room which is very big.
The rest of the hotel is clean and light.
The breakfast room while we were there was full so they had opened up a large conference room filled out for breakfast. This worked well and actually was better as the breakfast room did get crowded around the buffet bar.
The position of the hotel is perfect. It took 10 mins to walk to the old city but this was past lots of bars, restaurants and shops.
Well worth a visit.