Its a nice city to visit, good food, a lot of beers and chocolate to taste, really beautiful architecture. Didn't go to a lot of museums but there are a lot to know if you want and have time to. The winter may be cold but with some good clothes you are just fine and maybe can catch some snow if you're lucky!
Insider Tip:Rent a bike if it is possible, have a map with you 'couse there are no much of information in the streets and they language is impossible to understand hehe. Eat fries, chocolate, moules, try to drink as much beers as you can 'couse there are A LOT of them and they're really cheap.