From the back of the box:
Remember Tetris? The way those cubes kept coming at you? That was tricky enough, but what if they were half a dozen different hats instead? Derbies, baseball caps, cowboy hats, wizard hats, top hats and crowns? Well, that's the whole idea behind Hatris. The hats keep coming at you two at a time. All you have to do is stack them up five at a time and -poof- they're history. It sounds perfectly simple. Until you get into it. Then you'll wish you had six heads instead of one. Because this is the latest game from Alexey Pajitnov, the designer of Tetris, and his partner Vladimir Pokhilko. And anyone who could turn geometry into a contact sport is a force to be reckoned with. And this time they really want you to use your head. If you don't, you'll look pretty strange with that pile of hats on it.