Reaction games built around one idea taken seriously. Most are original rather than nostalgic, and the good ones remove something you expect to have. Backfire is a fixed-screen shooter in which you have no gun at all. Gravity Snake is snake with no steering: you flip gravity and it falls until it hits a wall. Echo-Location takes away sight, leaving you to navigate the dark by throwing rocks and listening, while trying not to be heard yourself. Short runs, immediate restarts, and a score worth beating.