Purgatory House is an excellent example of simple idea turned into an entertaining game. It pits a group of investigators/survivors against a house that is clearly there just to torment them. The gaming mechanics are kept simple by design so that Purgatory House works as a pick-up-and-play kind of game.
The essence of the book are the random locations of the House. They are vividly described giving the GM not only a fun game to run but a toolbox to be used in any kind of game where haunted house is needed.
As constructive criticism goes I think the game could have used a bit more coherent editing and maybe not so cartoonish illustrations. These both are minor details and do not hinder the actual gaming experience in any way.
To summarize - I really liked how this game takes a simple premis of a horror story and gives you the tools to run a quick game as effortlessly as possible. You do not even need maps for the house (and I would actually advise you against them). A solid gaming book.