DUCK HUNT
Duck Hunt is a browser take on the old light-gun game: ducks fly up out of the grass, cross the screen, and you have a short window to hit them before they get away. Here the gun is your mouse or your finger. Point, click, next duck.
Each round the ducks get quicker and their flight paths get less predictable. In round one you can track them easily. A few rounds in, they're zig-zagging, two are up at once, and you're deciding which to go for. Miss too many and the round is over.
It's a reflex game, plain and simple, and it rewards the same thing the original did: don't fire the moment the duck appears, wait a half-second until you know where it's going. Your score climbs with each hit, and chasing a personal best is really what keeps you playing.
It works with a mouse on desktop or a finger on a phone. There's no download and nothing to set up, and a round only takes a minute or two, which makes it an easy game to come back to.