Keylugger

From the author's description:

[...]you must transport a heavy key to a keyhole by jumping and throwing it. Your character can jump four blocks in height when unburdened, but only two blocks while holding the key. When the key is thrown, it soars horizontally until it hits an obstacle. Lasers and cannons will not harm the player but will cause the key to return to its starting position. And, there are some shutters which open or close depending on the player's proximity to them.

The above pretty summed up the game mechanics. They would be nothing without the brilliant levels the game has, each one very varied, different than the rest. There are no tutorial levels per se, so you have to think what to do on your own, which I appreciated - modern games tend to take you by the hand and explain the difficult stuff for you instead of making you find out on your own. Anyway, the gfx are functional, the game plays brilliantly (although the character did stick around at a few points without reason), I can't comment on the sound because I had it off.

All in all, a real fun way to waste a couple of hours!