Engaged to a Polish lady here.
Differences that come up to my mind are the following:

1. Phone: when we Belgians are done calling we are done. Polish people on the other hand from the moment they say "bye" it always continue as "oh btw, blablabla ..." and this can take a while sometimes :)
2. Food: Salads are always a must for lunch and dinner. This typical Polish and I welcomed it with open arms, as we Belgians do not eat enough salads in general.
3. Church Polish people are very traditional in terms of religion. You better do not have a lame excuse for not going to church on Christmas or Eastern... or every Sunday, while in Belgium people barely go to church these days.