Not too bad if you are a creative GM who wants to work on things.
I picked up this supplement a long time ago. I never ran the scenario, but instead just used the rules for the occasional Cthulhu game. As the years went by I used the Chaosium system less and less and forgot about it.
I am now running a Cthulhu game using the GURPS system and I needed something small to supplement my game. I won’t spoil any of the adventure called “A Restoration of Evil” for possible players here, but I will say its a decent low level start. If you are running it at a convention it will work well out of the box. If its for a campaign you will need to fill in a lot of things.
Now that the the rules are very outdated, I wouldn’t pick it up for anything unless you could get it used for $0.50.