Hard as nails on the default difficulty. By the end of your first arcade run, you'll get a sense that you have to balance throwing objects, using items, jumping to dodge, and grabbing the titular Power Stones to defeat your opponent. The levels do just enough to distinguish themselves from each other, mixing various grab points, environmental hazards, and obstacles to keep fights interesting. There are also quite a few collectibles to unlock, including 3 additional characters, some VMU games, and extra options and settings. Overall, very fun. It's unfortunate the game hasn't been ported to more recent consoles.