Depends what you want really – there are plenty of good restaurants within walking distance.
De la Vigne a l'Assiette, rue de la Longue Haie – although the room is a bit severe, good menu and wine list well above average.
La Canne en Ville on rue de la Réforme – great steaks, game in season, run by the same family for years who provide first class Franco-Belge cuisine.
Chez Marie on rue Alphonse de Witte (nr Place Flagey) has a well merited Michelin star and a great wine list. Lunch better value than dinner but that's a general observation.
These places are small and have their own local customer base so best reserve ahead. Totally different would be Le Quincaillerie on rue du Page –magnificently converted old hardware store with athmosphere and setting – food is ok if a bit functional but they do have a good oyster bank.
All have websites but for a wider choice look at www.sensum.be (Brussels is compact). Check for holiday closures during summer.
To add a few:
When I lived in Brussels, my absolute favourite restaurant was "Le grain de sel", located very close to your hotel (near landmark Place Flagey). I haven´t been there since I moved away in 2006, but according to recent reviews (Tripadvisor, resto.be) it seems to be going as strong as ever.
French influenced, daily rotating menu, 1-3 courses. The whole 3 courses is around 24 Euros, which is an absolute bargain in Brussels for food of this calibre.
Address: Chaussee de Vleurgat 9.
The whole Flagey area, especially Rue Lesbroussart has many nice eateries, e.g. La Cuisine (Rue Lesbroussart 85), practically around the corner from your hotel.
"Brussels is not big, but it`s deep" as my former boss used to say. It is a truly wonderful city, so I hope you have a nice time!