New Super Mario Bros. Wii has barely been out 48 hours, already there's a level editor for it, and already someone's rebuilt World 1-1 from the original Super Mario Bros.
This might be played through a Wii/GameCube emulator, not on the console itself. There are a few flaws in the re-creation — how many can you spot? Mario doesn't go into the subterranean coin chamber, but that doesn't mean it doesn't exist, so let's say that one doesn't count.
Fan Recreates SMB World 1-1 in NSMBW [The Tanooki]