Ostrava wasn´t really important place in medieval ages it´s obvious that even the local castle…read morecan´t be something amazing as we know it from some other parts of Czech Republic. It´s the coal mines what is typical for Ostrava, not the medieval history.
But still, local castle has its certain magic. It´s more like a cultural place these days. There are perfomancies in local amphitheatre and also couple of exhibitions. The biggest one is about fairy tales characters. There is not much to say about history so I guess that´s why armoury and other typical castle´s exhibitions are ok with with one room each (and not many exponates). Also more descriptions about certain things would be nice.
Anyway. I guess this place could be on your "to see in Ostrava" list.