Crowds are heavy, but the long waits are worth it. For my money, the house not to miss is The Walking Dead, but my companions also say Evil Dead is a classic. And the Bill and Ted's Show is spot-on this year, so don't forget to get some laughs with your scares.
Tickets are still available for the final weekend of October, Halloween Night (the MOST crowded) and the first weekend of November. Prices can vary, based on the day, and it's looking like many of the add-on options are sold out. Visit the ticket site for more information, and it's always worth a phone call to see if add-ons or special tours (RIP highly recommended, if you can swing the cost) have last-minute availability.