Here's a new thursday feature. As the name implies, there will be a new free web game posted every week that is good enough to be playable for a week as well as the reason I picked it.
The Game: Super Mario Bros. Flash
The Justification: I didn't pick this game just because it's Mario, as flash Mario games are common. I picked it for its level editor, which will make it last for a long time.
Play it: http://www.onemorelevel.com/game/super_mario_brothers_flash