Metro Siberia Underground
Biilled as a Retro Soviet Style Gravity Tunnel Game, this excellently-soundtracked Flash delight riffs off the old keepy-uppy helicopter idea. Thanks to Darwinia stylings and hyper-real undulating landscapes, it's entirely its own beast, and is probably the best thing you'll do with your browser today.
It involves just one button - Space - to add thrust to the cursor-ship, but tickles more joy-points in the brain than a thousand games involving 20 buttons possibly could. Find the full game after the cut.
If you can't get the menu to work, just click on the game bit with your mouse, then cursor keys should start a-cursorin' again.
It's made by one Tommy Salomonsson, his first since 2004's self-consciously Nintendian Super Bobby World., with art and music by Simon Stålenhag. Their next game is the mystery-swaddled Kingsmountain, and based on Stålenhag's awesomely twisted designs for it so far, I can't wait.