Mark Rubin said to Edge Online, in an interview, that the a few people in the studio had a Diablo-like game in development back when MW2 was about to release.
Side projects like this exist at Infinity Ward, too, they just don’t ever talk about them. Rubin recalls one such prototype built around the time of Modern Warfare 2, “a top down, isometric, sort of Diablo clone but with a sort of whimsical silly theme.”
“Yeah, sometimes developers need a little outlet for other stuff and we try to encourage that where we can because sometimes cool ideas come from that,” says Rubin. “That game in particular – it never got hugely far – was pure fun. We let developers do something fun and if it turns out to be something really interesting and new then we can try to get some people behind it and do something with it.”
Rubin said that some the ideas that come within these side projects – although those projects are never released or talked about – influence some decisions when making Call of Duty games/DLCs.