As mentioned, can be meh or can be great. Often the high point is a food cart or other such vendor. HTe one in Berkeley N. of the gourmet ghetto has great vegan/mexican thingies and ice cream.
There are some mushroom farmers that make the rounds whom I like and the flower sellers are often the best. There used to be a great orchid guy at the one in El Cerrito.
Any of the . N. Cal guys ever make it up to Marshal for the fresh oysters? THere is something rather satisfying about pulling them straight from the water, shucking a few, and throwing them back.