This is a great hotel. My room was very spacious, with a sofa and desk, on the top floor overlooking the main road; the soundproofing of the windows is excellent so no noise from the traffic unless you open the windows, and no need to do that at night with the air conditioning. The decor is traditional and of good quality. My only gripe, pretty minor, is that in some of the rooms the bathroom door opens right in front of the wardrobe and drawers, so to get to your clothes you have to close the bathroom door completely. I loved the touch of underfloor heating in the bathroom to keep the feet warm--nice even in summer. I think different rooms are decorated in different colors; mine had blue striped wallpaper which I guess made it darker but I liked it. Wifi internet access is free (a real plus if you need it since in many hotels that can add a lot to your bill).
The hotel is part of a boutique chain, Eurostars, based in Spain; it's smaller than most chains. When I was there in late July it wasn't very full (off-season for Brussels especially in the eu and surrounding area) so I got a great deal, plus plenty of attention, all staff most helpful--in fact at breakfast I almost felt there was too much attention, two or three of us eating and as many people providing service, just waiting for a chance to fill up your orange juice again! (At least that was true during the week, the service at the weekend seemed more lax.) The breakfast is expensive (20 euros) but with high quality ingredients. For other meals the restaurant is also delicious.
The hotel is right next to a metro stop so the fact that it's some distance out doesn't matter much as the journey in is very fast (unlike say if you were a ways down the Louise district, which is a nice area but only accessible by tram). It's ideal if you don't want to be right in the center. I was there by myself on business, and in that situation I just slightly preferred the hotel I stayed in right after this one, the Sofitel Quartier Europe (very different feel, ultra modern); but I really enjoyed the Montgomery too, and if I wanted a classy hotel on vacation with my partner I would choose this hotel.