Gregory Horror Show is based on the obscure Japanese anime of the same name. The game starts out with you wandering through a dark forest, where you happen upon an ominous looking hotel called Gregory House. You go in and are greeted by Gregory, the hotel manager who also happens to be a mouse. Gregory takes you to your room to get some rest.
While asleep, you are visited by the Grim Reaper who tells you that if you collect the souls from all of the other guests (twelve in all), you will be free to leave the hotel. If you don't, you'll be trapped in it forever.
The key gameplay of Gregory Horror Show revolves around navigating the hotel and retrieving bottled souls from guests staying there. Neko Zombie the cat shows you the control scheme of the game and is pretty much your tutorial, like spying and collecting souls. Spying in keyholes allows you to eavesdrop useful information on guests as well as coming face to face with the particular guest behind the door your spying in or not.
Guests will usually flee if you see them and while still possessing a bottled soul. Once you have recovered that soul from the guest instead of running away like lame-o's they are they will attempt to attack you and probably succeed. The guests can run faster than the protagonist which adds a really neat layer of depth, stealth, of course. You can hide in wardrobes but thats when someone isn't chasing you because you know you happen to take their soul.
The more souls you have the more guests and more hotels come in tact to explore and interact with. In addition the people you stole souls from will make it a pain in the butt to travel from hotel to another.