Some of the highlights of "Old Mazatlan" would be: the shoreline along the old downtown area and the cliff divers; the lighthouse at the top of the hill at the harbor entrance; the old opera house which is being renovated (or was in October-it may be finished by now) and the whole artist's colony that has built up around it; and of course the Cathedral and the old marketplace.
We thoroughly enjoyed the Papantla Flyers show at the Aztec Theater. The Flyers are just the finale to a very colorful and entertaining folkloric show. Just be sure to get a seat in the shade.
The Golden Zone, where the Aztec Theater is located, is a large assortment of shops, botiques, restaurants and luxury resorts right on the beach. It is in my opinion the best place for shopping on the Mexican Riviera; it has the best variety of stores and merchandise, and the best prices.