One Button Games

Give a game one input and everything else has to be design. There's nothing to blame - you either pressed at the right moment or you didn't, and the game knows which.

Zip Zap is the tightest of the three, built entirely around timing a single press. Sausage Game uses the constraint for comedy, letting the physics do the work your missing controls would have done. Click Click Clicker takes the idea to its logical end and makes the button itself the entire game, which is either brilliant or infuriating. You'll understand each of them completely within about three seconds, and then spend considerably longer than that failing.

There are 3 free games under this tag, all playable in the browser with nothing to install, and they're understood completely within about three seconds.

The precision end is Skill games, and Puzzle games covers the ones asking you to think rather than react.