I don't know Brussels that well. But I used to live in both Gent and Antwerp. Both are nice cities, the train fare is minimum. Belgium in general is very cheap. Gent is very beautiful, old buildings etc... The university is worldwide famous and you see students from all over thr world. Antwerp is also nice, with old monuments. The port is beautiful and groneplats, don't remenber how to spell it properly, is a very nice place to dine or have a nice lunch. There are few museums around and you have the famous Meir, a shopping street, not so expensive and at one of the ends you can find the local Market. Transportation is not so expensive, if you arrive at zaventeen, not sure if spelled right once again, make sure you take the train, it, the airport is bit far from Brussels itself, 30 to 40 mins so taxi would be a bit expensive. On train tickets something around £6. You can also take bus! Have in consideration French is spoken in Brussels so not much likely to find people who speak English well, unlike Flemish spoken areas. If you fancy going to the beach, even if it's out of curiosity there is an artificial beach in Belgium.
Some additional info: the shops in Belgium in general close very early, due to labour regulations, but some are exception like the Meir in Antwerpen.