I dare say, the best Cthulhu-based game since Call of Cthulhu and the Fantasy Flight line. The material is thoroughly researched and presented very well. Eight investigators to choose from, and you'll probably need all of them as the game does not hold your hand.
Repeat: There is no hand-holding in this game. You will lose, and lose terribly, until you learn how to win.
It's not a theme park game designed to let you breeze through encounters to ensure you see all the beautiful things they put into it. It doesn't give you a 'been there, done that' t-shirt for showing up.
It is very old school, as are all the 4AD books, in that they are meant to be challenging.
If you want a game you can play so you can say you did, roll a die. If it's a six, you won! Congratulations. Here's your shirt.
If you want a game that will challenge you and keep you on your toes, 4AtGOO is one to beat.