I rode DL's Haunted Mansion recently for the first time (albeit with the holiday overlay), and the Hatbox Ghost there happened so quickly before you turned towards the downhill into the graveyard. I just barely saw the transformation. Thought it was only okay tbh.
At least from the videos so far, in WDW's there's somewhat more time to view the Hatbox Ghost and appreciate it and the effect more.
How it affects the overall scene with the endless hallway remains to be judged. But from comments of people that have seen it today, the AA itself and lighting is good.