Gryphon Hill failed because it tried to be too many things at once - Dracula in London, Dr. Jeckyl & Mr. Hyde, a ghost story, attack of the pod people and the Hound of the Baskervilles at the very least. That might work for a 260 page campaign-length adventure, but it was too much to stuff into a 48 page adventure.
I think if it was reworked to follow this plot, it might work better (using the Deadly/Confounding Mists to wall them into town and slowly open areas up as they beat back Godfrey's hold on Mordenshire so they can visit the Weathermay House, Gryphon Hill, etc.):
Levels 1-3: The Sanitarium and the Town of Mordenshire (solve supernatural issues around town caused by individuals possessed by dead spirits caused by Godfrey returning the spirits from the dead)
Levels 4-5: Explore and expose the secrets of the WeatherMay House and it's lineage with a final confrontation with a Weathermay ghost in a sealed-off portion of the attic (sent by Godfrey to torment the Weathermays)
Levels 6-7: Raid of Gryphon Hill and confrontation with Lord Godfrey; discover that Strahd/Azalin have been pulling Godfrey's strings
Levels 8-9: Raid Heather House and face a Simulacrum of Strahd that is level-appropriate
Level 10+: Delve into the Mausoleum and confront Azalin and the apparatus