Arrows to move, one key to fire. Rows of shapes descend, you shoot up into them, and the gaps you make change how the rest of the formation moves. The presentation is minimal to the point of abstraction, which sounds like a gimmick until the first wave speeds up and you find yourself leaning in.
There is no story, no upgrade and no second mode. What there is is the original arcade cadence, the slow shuffle that quickens as the row thins, and the specific dread of the last invader crossing the screen at four times the speed of the first. Short sessions, high scores, and nothing between you and the game.