Imagine the traditional Call of Cthulhu game viewed through the lens of a cliffhanger serial, such as Buck Rogers or Indiana Jones, and you've got the idea.
That dangerous and dusty old book your investigator is carrying may come in handy (or may drive you insane), but the revolver your investigator is carrying will come in handy too ... and at some point during the adventure, you'll probably need to use it.
This sounds pretty cool! I need to look for these!
Yeah, Fin, I don't know if you meant it that way, but your question makes it sound like AoC is a separate game unto itself -- when it is a series of adventure modules.
Clearly a mis-understanding on my part, as I thought it was its own rules system. I didn't realize that these were modules designed to fit into the regular CoC rules.