I don't know how many FPS fans there are here, I'm not big on them myself. But I'm posting this one mainly because it's amazing to see how far games have come, and how the coolest, cutting-edge games from back in the day now run so well in little flash widgets in our browsers.
KEYS
W, A, S, D or ARROW KEYS - movement ; Q, E - strafe left, right ; SPACE - fire ; R - use door/switch ; SHIFT - run ; ESCAPE - menu ; TAB - map ; NUMBER KEYS - change weapon