If you have never been to Disneyland during Halloween, I highly suggest it, especially during September. It is slow season so most rides have wait times under 20 minutes, with the few exceptions like Radiator Springs Racers or Space Mountain. The crowds are minimal which makes it great for slowing down and enjoying your walk from ride to ride.
As you come up to the entrance of the park you will see the jack-o-lantern versions of the fab 5(Mickey, Minnie, Goofy, Donald, and Pluto). Once inside the park, all of main street is covered with fall colored decorations and pumpkins everywhere. There is also a giant Mickey jack-o-lantern near the Emporium that is a photo op and has Mickey's face on both sides so the lines to take pictures are not usually too long.