Had a great stay in Cityden with a few friends. They apartment was spacious, clean, and actually larger than we expected from the pictures. The building is well located in Amsterdam and a short tram ride away from the city's main attractions, while the neighbourhood has anything you might want during your stay including a good supermarket, coffeeshops (both kinds), and a shopping centre. Staff are friendly.
The one issue for us is that at night there were quite a few people outside the building who didn't seem to be staying in the hotel but simply hung around waiting for the doors to open. It was a little bit unnerving and I had to tell one of them quite strongly to step away when I opened the main door. Perhaps the hotel could do something about these people.