If it's anything like the halloweekends at cedar point expect people in costumes... spooky music... and thats about it oh and they play a movie on a huge screen... but who wants to watch tv when youre at a roller coaster park??
It depends on which SF park you're going to. At the Arlington, TX park, which is nearest me, they have zombies that walk the park, 3 or 4 haunted houses for an extra fee, and a couple of Halloween related shows. Plus, the park is decked out in spider webs and skeletons. Some years are better than others, but we usually go anyway.