I've been running Call of Cthulhu since 1981, and have more than four shelf-feet of published Call of Cthulhu stuff (including the original saddle-stapled version of this campaign). Of late I've been converting to PDF to enable me to prep games on my hour-long commute and reduce in-game table clutter, hence this purchase.
This PDF represents the expanded version of the original (and first) campaign for Call of Cthulhu, the version published in 2004.
I ran this in the original 1981(?) version and from a brief but targeted reading judge some segments to be now more challenging for the GM than the original. The Scotland episode is particularly over-the-top in infoload, and some of the reasoning presented to the players doesn't bear close scrutiny in the Silver Twilight section. You may have some work ahead if you need tight consistency in your game (and this is a detective-style game at heart).
Looking through my notes I see that the original campaign was extremely lethal, wiping out player characters with the ease of a gatling gun. The GM is going to have to do deep preparation and read ahead and make notes before running any of the episodes so he or she can mitigate the fallout where necessary.
That said, the players who went through the experience with me in 1987 had fun (or so they say) and certain events are trotted out by those "who were there" when we congregate on rare occasions. A GM can't really do better than have people talk about imaginary events as if they were real.
My low star rating is mostly because the standard approach used by Chaosium to make these PDF products results in a basic scan with OCR underneath but no bookmarks. This means a GM will have to "search" for everything he or she wishes to find in-game and weed the false positives for what he or she wants to see.
Bookmarks aren't a luxury in PDF RPG products, they are essential for flipping back and forth as the game plays out.
Better still would be adding an internally hyperlinked contents page as well. PEG and Pelgrane Press can show Chaosium how it is done.
But that isn't how Chaosium has made the PDF products I own so far. Even the brand-new Gaslight, a product born well into the 21st century and authored electronically, was sold in PDF form sans bookmarks.
It breaks my heart because these pre-"finacial collapse" products are extremely high quality in their concept and execution in print form, and this specific product revolutionized what people would come to expect in terms of hands-on clues and handouts from printed scenario/campaign RPG products. Literally a game-changing idea.
Given the lack of bookmarks, I think you will probably be working from highlighted paper copies of whichever part you are playing, like we did in the 1980s.
So three stars for overall quality and user experience.
If you are reading and are affiliated with the publisher, I'd have paid five bucks more for those bookmarks.