We stayed in Waterloo II in January and found it to be a very good base for a couple of days in Brussels. It’s located in an area surrounded by high-end shops like Gucci and Louis Vuitton, and very close to two metro stations. It took about 20 minutes to walk to the Grand Place from here, which took us through the Mont des Artes and past some of Brussels’ fascinating little streets.
The apartment itself is spacious, comfortable and well-designed. Not sure you’d really want to go there as a foursome: it’s definitely a nice place for a couple.