I ran the full marathon last year. It was OK. Of the dozen or so marathons I've ran, it was one of my least favorite. I think it would have been much more enjoyable if I was a first time visitor to San Francisco, but I'd been there dozens of times. I had heard that the course was extremely hilly; there was even an article in the Wall Street Journal about the brutal hills but I never really noticed them and found the course to be much smoother than marathons that don't even advertise themselves as hilly races (St Louis, Little Rock, Birmingham). I think the first half had fewer than the second, but don't really remember. I do know the second half course was boring and the first half was much more scenic. The golden gate bridge takes up a big part of the course.
The first half does not seem to be a good course to set a PR. Running across the Golden Gate bridge was very crowded and there was not much room to maneuver. It was so foggy that there was not much to see. I don't want to sound too negative about the race because I had a really great time and ended up running one of my faster races. The weather was by far the best part--compared to Midwestern summers, the cool race-time temps were amazing. Good idea to bring some throw-away clothes to ditch early on for sure. The race expo was nothing too exciting. I am generally not a big expo fan and I found it to be very crowded. Much better things to see in SF!
I am sure you will have a great time! Hope you update us on how it went.