Docked here - not very impressed shops and bars - Ocean Village took our cases the night before so we had no change of clothes and nothing to do for 12 hours until they sent us to the airport. Suggest if you are going to be here for the day, book something up rather than just wandering around.
I am sorry you did not enjoy Crete. There really are a lot of options in Heraklion including the wonderous ruins at Knossos and an excellent archaeological museum that has some of the most important Minoan artifacts in the world (many of which come from nearby Knossos). Crete is also a very large island where a rental car can open up lots of other possibilites.