I was wondering the same thing.
Anyways, what are the must-see / must-do's in Brussels?
Really depends what you're into.
If you like tourist traps and Japanese tourists, go visit Manneken Pis.
If you like big metal things, go visit the Atomium.
If you like museums, there's plenty to do: the Magritte museum, the music instruments museum, the Royal Museum of Fine Arts, ... etc. Near Brussels, in Tervuren, there is also the Royal Museum for Central Africa.
If you like to eat, plenty of places to go to as well. Go eat an authentic Brussels waffle near the Grand Place. Try "carbonade flamande" (
https://en.wikipedia.org/wiki/Carbonade_flamande). Lots of good food out there. Many beer cafés in Brussels too, so if you like beer, be sure to go try some Belgian beers.
If you like architecture, make sure to follow the Horta tour:
http://www.arau.org/en/t/8-totally-horta/8
Keep in mind though the Brussels is a bit of a difficult town to "grasp". It's not immediately appealing. Actually, it may even be a bit off-putting at first. If you want to be wowed at first sight, do as Ringo suggested and go to Ghent or Bruges, maybe even Antwerp. Brussels is not like that. It's a town that, due to its history, requires you to put an effort to seek out the good places. They are more scattered throughout the city.