Stayed 3 nights at the Dominican in early January. It is a nice little hotel but definitely not a 5 star property.
We stayed in a standard room which is really on the small side ( 24 sqm) and is really only suitable for 1 adult. Nicely designed with big LCD screen, Nespresso machine and free internet connection. Bathroom is shower only, one sink and no separate toilet.
There is a small gym with cardio equipment only and a sauna.
They serve a great buffet breakfast in the main restaurant. I am not a huge fan of buffet but I really enjoyed it. Did not try lunch or dinner.
Service is quite friendly but don't expect someone to open doors or carry your luggage for you.
Brussels is a real hotel desert and all in all we enjoyed The Dominican and would stay there again if I can get a good rate. But if you are really looking for a 5 star experience I would choose the Amigo.