Contains some spoilers!
In general, it is a solid and engaging introductory adventure, but requires still some preparations before the game.
There are a couple of little things that preclude me giving a perfect 5/5 rating:
Most annoying one: While the scenario comes with nice maps and all, the Glenridge city map can not be handed out to players until after they have found all the clues in it.
Secondly, there are not many NPCs for players to interview. There is one primary clue pointing out to the perpretrator, but I'd like to have alternative ones and one can imagine how to provide them (victims' families, friends, etc could provide them). Again, this is something any GM can come up with by themselves, but it would be nice to have some more flesh.
Also, as a matter of personal taste, I myself do not think it fits that the "cosmic terror" aspect that humans would be being able to control and command Mythos creatures (feels to DnD-like to me), but that can be again easily changed: I personally adjusted the scenario so that despite what some people think (They are deluded), cosmic terrors do not care for orders and commands, they listen to suggestions.