If your're not familiar with Rotterdam you should anyway try this restaurant. It is not glossy, it is not 4 * but the plain vanilla dishes are simply good and especially fish cannot go wrong.
I can advise the fried mussels (superb today).
If the weather is good you can sit outside and enjoy the view at the harbor, if that's not possible
it is inside cosy and a lot of rumor for free.
From lunch to dinner, most of the days always quit busy.