No one has mentioned the nicest area in the city, which is old Mazatlan. Take a walk there. You will see art galleries, museums, the Machado plaza, the Angela Peralta theatre and many sidewalk cafes. It is a 5 to 10 min ride away from the ship by taxi and the cost should be around 5us. per taxi one way. Then from there, walk down to the cathedral and market where there is more to see.
There is a lot to see in Mazatlan, but you have to go to the right places. The golden zone is nice but it is the american side of mazatlan. Old Mazatlan is the mexican side of it.
Enjoy Mazatlan amigos!