Now this one is nicely done, although its just a presentation demo and consists only of a small part of the first quake level its astonishing what can be achieved with macromedia shockwave this days.
I suppose everyone knows the original quake game which was fun to play, especially because of the coop story mode part where you could play the game with your friends in coop mode.
Take a look at this great remake, and keep an eye on it, if they continue it will become an excellent conversion.

Quake II Evolved
Castlevania Flash Game
Fun Game Sonic
Incredible Flash Adventure Game
Defender of the Crown Flash Game
Weekend Game Streets of Rage Remake