Radius Raid is a sharp little javascript + canvas game made by designer & developer Jack Rugile (@jackrugile) for this years js13k games competition.
Reminiscent of asteroids, as well as the more modern geometry wars, radius raid has you flying a small ship, defending your self from hoards of spherical enemies, and performs more than admirably (a consistent 60fps for me) for a javascript based game, built entirely on the canvas.
The controls are a little tricky to get a handle on at first, but once you’ve got them down, the game plays fantastically.