Although I've never been to the Saturday market, I'm a regular at the Tuesday market, run by the same people with many of the same (although many fewer) vendors. This market has also moved from Justin Herman Plaza to the Ferry Building.
Plusses: better flow around the stalls; a couple of new vendors (Zuckerman has set up its fry station -- yum!); seems to be better attended.
Minuses: Dangerous! Since this market attracts mainly office workers, large numbers of pedestrians are crossing the Embarcadero, which involves two sets of traffic lanes and the Metro tracks, all with separate lights. Many, many people were crossing against the lights, including me: the crowd had surged across the street and I followed, not realizing the light hadn't changed and there was fairly high-speed traffic approaching the crosswalk with a green light. They need to cycle the lights more quickly so people don't get impatient; even better, they need someone directing traffic out there on Farmers' Market days.
Still, I think once the Market Hall is completed it's going to be an asset to those of us who work downtown or pass through that area on our commutes.