Premise: Trashville is about to be engulfed by a pile of garbage. You need to step in and improve their waste sorting! As the waste comes down a conveyor belt, drag it into the correct bins (compost, paper products, and containers). You win points for every item you correctly sort, and lose points for incorrectly sorted items (which also fall back down to the conveyor belt). Once three items fall off the end of the conveyor belt, you lose (Trashville becomes engulfed).
As the population of Trashville grows, it produces more and more waste, and it comes down the conveyor belt faster. If you can sort out the oncoming trash fast enough, the giant pile of garbage will degrade and you save Trashville!