I ran the classic Call of Cthulhu scenario The Haunting with my D&D group over a two nights as an interlude in our usual Age of Worms epic campaign. I'll skip over the story details because the haunting has been covered so many times already.
Rules-wise, I used the core Call of Cthulhu BRP rule set, summarized to a page cheat sheet for the players. Additionally I tried to apply concepts from Trail of Cthulhu and the Burning Wheel family of games. Ideas like Let It Ride and Core Clues I explicitly used. The general flavor of how Trail and Burning Wheel treat dice rolling and failure held for a lot of the game. My favorite ruling was quietly using the Enmity Clause when the players were effectively circling up a back alley doctor to help with their (self inflicted) gunshot wounds.
Beliefs; We played a pickup style game. I made 7 pre-gens for 5 players, only one character outline was provided for me. Each character was bare bones attributes plus skills, and a weapon of some description. Instead of writing complex back story for each character matt and I cooked up 2 or 3 beliefs per character and I handed those out when players selected characters. The players did a great job of taking the general shapes of characters and fleshing them out. There was a lot of great drama and conflict in the party that really built things up once they action reached the house.
In addition to the Beliefs, I managed to restrain myself at the start of the game and give the characters a few minutes to role-play introductions and flesh out their characters in game. Worked great, I'm sure I'll use this technique again.
The prop newspapers and photos I spent ages making worked great. They should hopefully be going up on Yog-Sothoth once they have had a final edit.
What could have been better
There were a couple of scenes where I lost hold of the BW/ToC ideas and slipped back into more traditional style and framed scenes poorly. In particular the Chapel of Contemplation scenes were very weak and full of whiffs.
The end of the scenario felt quite anti-climactic; I don't know whether this was because it came after the confusion and drama that started with upstairs bedroom and continued down in the basement, or because its just not a very exciting final scene after all that has gone before it.