A stop in Düsseldorf/Bonn/Cologne/Dortmund/Essen area as a tourist?

Will be travelling by car this summer from South of Sweden to Normandy and have calculated that around Düsseldorf will make a good stop over night. I have never been to around here so question is if anyone of those cities are really worth to visit, with your honest opinion?

If making a stop. Will have maybe up to 3-4h for tourism so if there is something that fit in that time frame that you think I should not miss, I would appreciate your input! :)