This game has an incredibly simple premise, but it's extremely satisfying and creates that "heated brain" feeling from figuring it out. Basically, you're shown a collection of cards with symbols, and you have to select three that form a "pack." Packs are either: cards with two matching categories (out of three: number of symbol, shape of symbol, and fill style of symbol), or cards with NO matching categories. The faster you find packs, the higher your score. A quick play round has about 20 cards at the beginning, so if you're doing well you can find all the packs within a minute or less. But there's no active / visible timer, so it doesn't feel rushed. Great challenge, great satisfaction, great game.