Before you could tell he was a plumber . . .
MB provides players with a simple formula, stun enemies by hitting them from below and then knock them off the course. You face a number of different enemies, but the only one to move on this game was the koopa troopas. You also had crabs (which you could argue moved on), fireflies, and icebergs. In the middle of the course, there was a pow box that would automatically flip over any enemies that was touching the ground. Occasionally, you would stumble onto a mini game of collecting coins before time ran out.
While the course never change (minus getting slippery), the game provided combinations of the different enemies and a multiplayer mode that introduced Luigi to the mix.
Interesting to note is that this game started a franchise that the little plumber never predicted. While he first officially appeared in Donkey Kong, Mario developed his own series of games on the NES and continued to become the icon of Nintendo. The original game even became a part of other games in the series, to remind players of the roots of the dynamic plumber.