1. In the words of Rudyard Kipling, What can he know of England, who only England knows? Getting out of the UK (or the US) will open up your perspective and help you better understand yourself and your own culture. The things you thought were indispensable (shops that are open when you need them, iphones, decent-sized lattés), you will discover you can in fact live without.
2. Brussels is a lot like America. No, really - hear me out. Ask the average person in Brussels where they are from and they will respond as if trained to be elusive at spy school - "well, it depends what you mean by from, exactly...". I've heard it said that New York is full of people with allegiances to two places, and Brussels is like this too: the home par excellence of that strange species, the Third Culture Kid. If you belong to this grouping, it's refreshing to find somewhere that's brimming with people like you.
3. Belgium is strategically placed for travelling around Europe. For such a tiny country, it does well - sharing borders with France, Luxembourg, the Netherlands, and Germany. Easy to get everywhere.
4. If you're a language geek, it's heaven. Everything's always at least bilingual.
5. The waffles, the chips, the chocolate.
6. You will make friends from many different countries, who will then go home, leaving a trail of invitations to visit them in their wake. Bargain!
7. It's the place to be for international politics, or at least the European variety thereof. Washington DC probably just about has the edge overall, though.
8. People are nice. Not the people paid to be nice to you, but the average person on the street. They say hello when you walk past them; they help you work out which bus to catch and which metro stop to get off at. People at tills wish you bonne journée after you've paid. All very civilised - in those ways at least.
So there you have it... And of course, there's always the fact that I live here, and I'm always happy to make new friends...