Only been to Brussels and Antwerp now, but nevertheless:
The Good
The Flemish accent is pro. I love it. You people have got some hilarious words in there (poepen in Flemish, neuken in Dutch, I saw this during Watchmen. Flemish subtitles ftw. I had to keep myself from lolling).
Brussels public transport is made of win. Trains every 5 minutes. Squeeky clean subways. Everything runs on time. The subway trains aren't even vandalised, which is pretty much standard in the Netherlands. Cushioned leather tramseats WITHOUT knifemarks? Good job.
Brussels as a city is awesome. Whether you're having a night out on De Brouckére (which feels like a European Times Square) or you're sniffing culture at De Grote Markt, it's amazing. The architecture of Brussels is -phenomenal-. I also like how modern buildings are built -around- medieval ones, to preserve the city's character. Job well done.
The people in Antwerpen are very nice. Whereas I experienced some slight anti-Dutch sentiments in Brussels, the Antwerpenaren were all friendly and polite.
Smaller Flemish towns have more "Frituren" than you can shake a stick at. I also like how they don't really feel like you're driving around in the 21st century. Most smaller Flemish towns have this 18th century feel to them for some reason.
Lots of police about patrolling. We even got a talking to just for hanging around at a statue.
Waffles. Nom nom nom.
The Bad:
It took us two days to find a Frituur in Brussels. Such a hard time finding Vlaamse Frieten in the Belgian capital? What's up with that!
The Belgian roads are... not that good. Of course, as a Dutchman I'm somewhat spoiled since our roads are too pro. 8D I just found it amazing how as soon as I cross the border, the asphalt gets noisy, the roads are bumpy and filled with holes and the roadsigns are sometimes vague.
It appears that Dutch is no longer a factor in Brussels, which bothered me. I had hoped for the city to be a bit more bi-lingual. Nobody at all spoke Dutch.
Belgian houses are a bit strange. It's like people randomly took plates of metal, bricks and a bunch of nails and started throwing buildings together. In Holland everything is so structurised and neatly planned out. In Belgium, every building is different from its neighbour.
Conclusion:
All in all, I had fun. Brussels, despite its Frenchiness, is definitely a place to return to. Antwerpen seems worth exploring a bit more but it did feel a bit cold and distant (the city, not the people) compared to its bigger capital city brother.
Belgian people are among the most kind and polite I've had the pleasure of experiencing in any country in Europe. You're currently ranked #2 on my politeness list, with #1 being Sweden.
It would seem that 1839 only did you folk a lot of good