As far as I know this is the unique restaurant named Beijing Roasted Duck in Madrid which really makes you excited. It's decorated well which is more modern, more european than the other Chinese restaurants except it's a little small. Their dishes are also fine, it's quite worthy trying the duck, although it's not the authentic Beijing Duck, it tastes very good. It's a little bit more expensive than the others, about 25 euros per person.
Personally speaking, I don't like it very much because it's a little bit small for so many tables, and the plates sometimes come with a dirty back. And the dishes come slowly. However, if you wanna eat roasted duck in Madrid, here is your choice because their duck is good.