I’m going to shock some people. I’m not going to pick Cthulhu. Everyone knows about Lovecraft and Cthulhu is a good setting a good system. But for being the flagship horror games the scariest thing is that your character is weak and its monsters are immensely powerful. There’s not a lot other than the sanity chart to conveying the fear that comes from a Cthulhu game. Everything after that is left up to the GM. There is nothing wrong with this. Yet I think that there now are other systems that help the GM make the experience better.
I gave it some thought and I’m trying to decided what game has the ability to best convey the fear and the consequence of horror in a game. As well as having the support from the system to do it well. That’s when FATE came to mind. FATE adds a lot to the narrative of a horror game as a whole. Aspects bring so much more to the table in a game where you want your players tense or fearful. Picking the right aspects can completely change the mood of a scene. Then you have Health Tracks, with three base health tracks you can affect stress and damage with s a bit more precision than in CoC. This brings us to consequences. With consequences you now have the ability to set short and long-term mental conditions on a player. That can last for sessions upon sessions of the game or permanent if extreme enough. Much like sanity loss but in a far more detrimental immediate way. This is where it sets itself apart from call of Cthulhu.
To me in a horror game the thought of a player having to describe to me how they take themselves out of the scene by fear and injury. All the while they know that if they take anymore damage and are taken out. That the GM will get to describe how they are taking out of the scene really adds a great element of tension to a horror game.