Balloon FIght is an instant classic that will never get old.
I don't think it's is relevant to talk about graphics now, this game is old, graphics are VERY, VERY simple, even for the NES standards, the animations of the sprites are pretty decent though. But, one thing NES teached us all is, that is possible to make awesome gems with the most simple machine and graphics.
The music and sound effects are very cool, and the rules are simple, just blow up the enemies balloons and try not to loose yours. Single player is fine, and can get challenging at times.
The balloon trip mode add some more challange and replay value, but the real fun of Balloon Fight is playing with a friend.
It's just plain fun, an old classic that is still worth playing.
Even if you are young enought to be not so familiar with NES games, I would recommend you give this one a try.