I think d20 CoC gets more flak than it deserves, and it’s actually a great case study in the value of system familiarity. Some of my fondest gaming memories were with d20 CoC. Yes, the mechanics were a terrible fit, but the book was excellently written, and for someone like me who wanted to try CoC but was too intimidated by the system at a time when I was still learning d20, it was a fantastic “baby gamer’s first horror RPG.” The horror really came from the buy-in; we played by candle light, with creepy ambient music, the narrations were evocative, and to a bunch of kids who had only played D&D before, our characters felt incredibly fragile and vulnerable.