The Convergence
A fun platform game with a twist.
Another World JS - Megidish.net
Quite astonishing use of canvas: the game Another World ported to JavaScript.
Related links
The Space Game
By playing this canvas game, you can help the European Space Agency plan missions to the planets of our solar system.
Akihabara
A framework for creating old-school arcade games in the browser, using HTML5.
LAZEROIDS!
Asteroids implemented using HTML5's canvas.
Geometry Wars
Graham is recreating the (beautiful and addictive) Geometry Wars in canvas.
Best played with a twin-stick controller (or WASD + Arrow keys as a fallback)
If you’re on Windows, XBONE or XB360 controllers are the easiest to use. On Mac, a PS4 Dualshock 4 or wired 360 controller (with a downloadable driver) works well.