I can't say much about Rijeka because I was there just for one night and I hardly saw the city in daylight. Nevertheless, I was lucky to make one of my favourite photos ever in Rijeka's main street. It is the photo with the fire truck which was just unfolding its ladder in order for an advertisement to be removed from a building.
Otherwise, in Rijeka there is a lot of water and there are many vessels – it is Croatia's largest harbour. You can feel a slight air of socialism, but the center of the old town is very beautiful. The symbol of the town is the Clock Tower which you cannot miss.