Dillo Hills 2
Both say right away, this multiplayer racing game is a big crush and certainly one of the best online flash games of the year.
Somewhat confusing during the first seconds, Dillo Hills 2 turns out to be extremely simple. You only need up and down arrows to "steer" your creature and the principle is to jump then adjust your trajectory to always fall back on a downward slope so as to increase your speed.
The interest of Dillo Hills lies in its multiplayer mode that automatically forms 8 players races with people all around the world.
And furthermore, Dillo Hills 2 is free, can be played in full screen and allows you to register easily (only a username and a password) to keep your progress and use your points to buy multiple upgrades.