It's retro goodness any man, woman or child can immediately pick-up and play
It's laugh-out-loud fun to play with friends
Mario is one of the best known brands in the world
Super Mario Bros was in 40m households on NES and this is tapping into all those that remember endless playing that game in the day. Huge nastalgia factor.
NSMB on DS is another 21M audience it's tapping.