Look at the pictures in my signature below. See the giant Mickey pumpkin and the giant Candy Corn? Only in fairly recent years has DLR really started to play up the Halloween thing and make Halloweentime a fun season at the parks. They've had Mickey's Trick or Treat Party for a while, I think, and the controversial Haunted Mansion Holiday began way back in 2001, I believe (possibly before that), but only in recent years did they begin putting up the giant pumpkin on Main Street in
Disneyland (in the same location where the Christmas tree is during the holidays) and the giant Candy Corn (located in Candy Corn Acres) over in California Adventure. Also, you will see a cool Day of the Dead display over in Frontierland, and last year there was a Halloween tree - also located in Frontierland. The Big Thunder Ranch location is transformed into Woody's Halloween Round-Up, where you can get photos with Woody and other characters, as well as decorate Halloween cookies and buy special merchandise. There are all kinds of awesome jack-o-lanterns decorated as different Disney characters, spread out around the Partners statue and in Candy Corn Acres. There are also all kinds of other decorated pumpkins at the entrance to DL, along Main Street and at the Round-Up. They sell pumpkin cookies and fudge and muffins (with Mickey pumpkins on the top) at the bakeries. Special, rarely seen, villains come out in DCA and pose for photos in the Hollywood Backlot area. There are even more villains who come out for the Trick or Treat Party, as well as other characters. For a couple of years, they even did a Pumpkin Mickey floral arrangement right at the entrance to Disneyland, where the regular Mickey floral display is year-round, but they skipped it in 2008.
It is really festive and fun. The parks are not as thoroughly 'done up' as they are during the holiday season, and I still prefer the Christmas/holiday season over Halloween, but since DLR has started making a big deal out of Halloweentime, and since the Haunted Mansion Holiday has become a regular fixture of the season, I really enjoy visiting the parks during that time of year. I actually hope DLR starts to do more for Halloweentime in the coming years, and starts getting even more elaborate with the decorations.