Brussels is great for a couple days but thats about it. One thing I would say for it is that it is a good place to end a trip because it is easy to get into, easy to get to the airport and the city is "manageable". When I am on the last day of a 21 day trip the last thing I want is to deal with the crowds, congestion, etc of Paris or London. If you do end a trip in BRU and need to spend the night I highly recommend the Montgomery Hotel, it is relatively close to BRU and in a nice quiet neighborhood near EU and NATO, feels like a private residence, very relaxing.