Most levels are waste space. There are various forms of wall, floor, and ceiling, the bits surrounded by them are for the character to play in, and the rest is just there as decoration. The non-used bits are generally leveraged to provide as much world-building as possible, but from a gameplay perspective it still ends up as negative space. Noita is a side-view action roguelike where “every pixel is simulated”, which in practice means there’s no section of the level that can’t be destroyed in some fashion.
Noita features a wizard-like character whose objective is to get as deep into a cave system as possible. While he’s got a staff that can shoot whatever magic you can find or create, the real power in the game is the many ways the environment can be persuaded to act on itself. Shoot out the wall on a tank of acid to melt enemies below, ignite the gas in the air to send a wave of fire through the caves ahead, cast a rain spell above a sea of lava to build a thin rock walkway while hoping the enemy isn’t smart enough to break it from under you, etc. The poor wizard is going to die a lot, but each death is a lesson towards how not to let that happen next time. There are more ways for things to go horribly wrong than chaotically right, but half the fun is learning how the elements interact and coming up with a new strategy to use them properly. As for the cave system everything happens in, it’s never going to be the same after the wizard’s gone though. Check out the new trailer to see what kind of destruction takes place when everything is potentially destructible.