First things first: I really like Call of Cthulhu. Mechanically it's very similar to Dungeons & Dragons, albeit with percentage dice rather than a d20 as the main ones you use, and the character stats and skills work in much the same way as their D&D equivalents. The big difference in terms of gameplay is that there's a lot less faffing about with the combat, which is a very nice change. Tabletop RPG combat can easily end up being dreary and tiresome, especially in D&D 4th Edition where you spend most of the time flicking through sourcebooks trying to remember what all your abilities do, but Cthulhu's is simple, fast, and often extremely tense because fights tend to be pretty difficult.
Naturally, the biggest draw with Call of Cthulhu is the one present in the name: the fact that it's a horror game based on the fiction of H.P. Lovecraft, arguably the most important horror writer of the 20th Century – and it's in the horror where the system really shines. As I detailed in my last post on the game, it's very easy for things to go spectacularly wrong very quickly, and character death is an omnipresent worry – in the foreword to the famous campaign Masks of Nyarlathotep, which I really want to play, the author outright tells you that the characters are unlikely to survive to the end. It's a really nice change from being the heroic adventurers of D&D where success is assumed: here, you're just ordinary people up against forces so overwhelming and otherworldly as to be practically inconceivable, and failure is a very real possibility.
Unfortunately, though, there is a serious contradiction inherent in the idea of merging a tabletop RPG and the Cthulhu Mythos. By their very nature, RPGs are founded in mathematics, because there need to be defined rules for how the game works or things would go off the rails even more quickly than they usually do. Numbers are the most concrete, logical means of understanding the universe that we have – there's a reason you can't do physics without doing a hell of a lot of maths as well. The problem with that is that the fiction of the Cthulhu Mythos is defined by its incomprehensibility and illogicality: what makes the monsters of the Mythos frightening is that their natures and motives are simply beyond human understanding, and their physical appearance is often beyond the ability to describe.
In the story from which Call of Cthulhu takes its name, we have no idea what Cthulhu is, where he's from, what he's doing, or why he's doing it. That is what makes him frightening. In the game itself, Cthulhu is defined by numbers and statistics: his motives may still be vague, but the GM knows precisely what he is in game terms. Even though he regenerates them, the very concept of hit points, that most crucial of role-playing concepts, is antithetical to the Mythos; the idea that these cosmic abominations will die if you do precisely this much damage to them is profoundly problematic in terms of what makes Lovecraft's fiction so compelling.
Let me stress that it doesn't make the game any less fun, and I'm certainly not trying to put forward a solution. For me, this paradox is pretty much insoluble, because tabletop RPGs are and always have been grounded in maths. It's just one of those irritating things that stick in the back of your mind, and I thought it was an interesting point about the game. It's not as if I would want to change the way things are: Call of Cthulhu is a fantastic game, and if this contradiction is necessary for us to be able to play it, then so be it. But still, it would be interesting to see if anyone could design a game which doesn't run counter to one of the most fundamental tenets of the Cthulhu Mythos.