We just spent two days in Manzanillo on the way back from Colima and lake Chapala. They have been working on the waterfront area for the last few years and it's finally in nice shape. You can walk the Malecon from downtown to near the port entrance (2 kilometers +/-). The cruise ships dock just past the Port Captain's offices. That's also where immigration is located.
The new Malecon
The new Portales
Front of the Mercado Central
Inside the Mercado
One of the hillside streets that are only walkable