Super Mario Bros. is a classic, and it's no wonder it's on the top of my NES list. Miyamoto had created two fine games with Donkey Kong and Mario Bros in the arcades. But this on NES, was something that blew everything out of the water.
Probably not the best looking NES game (btw the clouds and bushes are exactly the same!), however it is one of the best in terms of gameplay.
We've all practically played this one to death except maybe some of the younger kids who are reading this. I really shouldn't even have to write why you need to play Super Mario Bros.
It may not have the flashy graphics of the sequels, the countless power-ups, Yoshi riding, or maps, but it's still one of those games I can pick up every few years and play till the end like I was still a 2 year old playing with my Dad and brothers in the early 90's.