Help Waldi Vollgas with their trip plan: Going to Dusseldorf for Business
Depends on if you've been to other major German cities.
As someone who lived in Bavaria for three years and had traveled around Germany, I found the Altstadt disappointing. There was a lot of construction with roads torn up and I ended up taking an earlier train than I anticipated simply because I ran out of things to do.
I had lunch at a nice place, but that was it for me. Perhaps others have a different experience.