Best Nintendo game ever made...
Once you've run out of lives on one end, the other player than tries to go 'fishing' for the behemoth who will jump up out of the water to eat you.
I think while in college we played this game almost every Friday night for years as a drinking game :P. All in all, this is honestly the best game I've played for NES in the pure fun times department.
Also, there is the Balloon Trip mode which is incredibly fun. The whole point here is to go as long as you can and pop as many balloons as you can without hitting any sparks. If you've only got yourself around, this is a great way to burn some time :P.