The Unfinish'd is a tower defence game about a world that was never finished. Each level is a page of it: a floating island of written ground with a World Anchor holding it together and a tear in the page that the Unwritten climb out of. You build along their road, hold the Anchor, and try to keep the page from coming undone.
The twist is the ground. It is not scenery - it decays, it falls into the Void, and you can cut it away yourself to drop what is walking on it. A page you finish with holes in it still counts, so long as the Anchor stands.
The only thing that ends a run is the World Anchor's health reaching zero. World Integrity falling to nothing is grim, but it is not a loss.