my most recent Cthulhu game, I blurted out, for some reason I forget now, that I'm not using any pre-published materials in the campaign. Stephen asked me why, and I gave a rushed and garbled reason. Since then, I've been thinking about it a bit more, and I thought I'd put it in writing, since that's what blogs are for, after all.
I told Stephen that I don't use published Call of Cthulhu scenarios because most of them are "rubbish", and that one of the regular players has read or run most of them anyway. The latter is more or less accurate, but I at once regretted my sweeping statement about the quality of the scenarios.
A big problem with most published CoC scenarios is that they follow a pretty standard format. The players are called in, they do some investigating, then BAM! they run into some big wibbly thing from beyond space, usually a Great Old One or Outer God. Back in my first run as a CoC GM, I had one book, The Stars Are Right!, which was a bundle of six or seven adventures, all but two of which involved such large scale threats. Azathoth turns up at the end of one of them, for crying out loud! Now this mimics Lovecraft's fiction quite well, as Randolph Carter aside, he wasn't very interested in continuing characters and ongoing narratives. That's not so good for a campaign, though, especially if you want a slower, more subtle curve from blissful ignorance to full cosmic horror.
A related problem is that there is often little invention involved in the published adventures. The entities encountered are almost always straight from the rulebook or one of the stories, which is nice and authentic, but causes disappointment at the table when you go to lots of effort to describe the strange sound of flapping alien wings, just so one of the players can go "Oh, it's a byakhee; these are easy to kill!" Yes, you could change the entities encountered, but in the well-written scenarios, things are tied together in such a way that swapping Y'Golonac out for some minor servitor would make nonsense of the story, which would require a total rewrite, which would make using a published scenario pointless. As for the weaker scenarios, there's no reason to use them in the first place.
So that's why I'm writing my own scenarios for the current campaign. It means that I'm in full control of the pace of revelation, which is what CoC is about, after all. I've also tried to steer clear of using the iconic monsters, or at least to avoid using them in obvious ways, so as to keep both newcomers and veterans speculating on just what that is crawling around on the roof. All in all, it seems to be working out well so far.
All that said, it is only fair to give credit where it is due, and a lot of the published adventures are quite good. The campaigns are also, for the most part, strong pieces of work, and their pacing is much more to my liking. I don't discount their use in the future, but I can't do much with them at this point, and to be honest, I'm having lots of fun writing my own stuff.