In Hamburg we had about 10 hours time so we took the hop-on bus from Main station. It was interesting, just be careful which line you purchase, some of the (line A Blue bus) takes forever (about 1.5 hours) and takes you outside the town for some lake tour.
We also did the tunnel below Elbe, which was interesting.
Due to limited time (docked 8.00am-3.00pm) we took the canal bus hop-on boats, which was very informative, took us to the places we wanted go (museums mainly), then we went for a short walk in the center. I expected more from Amsterdam, but it was ok.
Nice touch is that the cruise port is about 15 minutes walk from city center, you are docked in the town itself.