The Rialto Bridge is the most famous and fanciest of the bridges that span the Grand Canal. it is lined with shops selling mostly touristy items. Murano glass, a Venetian handmade glass full of beautiful, vibrant colors and is the item that Venice is best known for, is claimed to be sold everywhere. However, especially around the Rialto Bridge, it's authenticity is questionable. Basically, avoid shopping in this tourist trap. Wander farther from the bridge and get some good photos.
Nearby, is the Rialto Market, with vendors selling fresh seafood and produce. I love strolling through food markets - we loved seeing the giant, fresh asparagus! Still though, it's less fun when we aren't buying anything.
The best parts of the day were when we were just wandering around the small narrow canals and tiny bridges. Really though, anywhere there were shops or restaurants, there were swarms of people. You have to get to the residential areas to really appreciate Venice. But, then there's literally nothing to do but wander around because there are few, if any, businesses around.