Al, you went to the wrong beaches. I have spent a lot of time on NJ beaches, as well as Ca. beaches. They are on opposite ends of the spectrum.
I've only been to a handful of beaches in Calif, so maybe I've been to the wrong beaches too.
I've been to Malibu Lagoon State Park, which I thought was a nice beach, and not too crowded at the time I went (which was a weekday afternoon). The scenery, with the mountains behind you, was certainly more interesting than NJ beaches, and I also liked the topless girls. But I don't think the beach itself was as nice as Island Beach State Park in NJ.
I've been to Santa Monica, but mainly to see the pier, which I thought was incredibly disappointing compared to boardwalk amusements in NJ. The beach itself was neither nicer, nor significantly worse than most urban beaches in NJ. I'd really give the edge to Long Branch, which has nicer beachfront amenities.
I've been to Venice Beach (on the same day I went to Santa Monica), but that was mostly to see the freaks. I will grant that it is freakier than Seaside.
I've been to Manhattan Beach. There was absolutely nothing distinguishable about the beach.
The unique thing that I noticed about California beaches is bigger surf, since it is a west coast beach, and the mountains in the area near Malibu. The unique thing about NJ beaches is the boardwalks, even without amusements in places like Spring Lake or Avon.
Also, since so much of NJ's shoreline is barrier islands, in many shore towns you have the beach side and the marinas on the bay side. While this is fairly common on the east coast (and makes up a good part of the Intracoastal Waterway), I don't know if there is anything comparable in California.