Hm.
Well, Ice Climber and Balloon Fight were two of Nintendo's first Two-Player simultaneous-play games. Most other games at the time usually made one player wait while the other play took their turn, and then they'd variate.
But in both Ice Climber AND Balloon Fight, you could compete AND cooperate at the same time. For example, in Ice Climber you could bounce off your friend's head to get a better jump. While in Balloon Fight you'd get a higher score by hogging all the 'kills' for yourself... plus popping your friend's balloons is always good fun.
Both games also featured quite a bit of music, and a similar play mechanic. A main stage area, and a bonus round of some sort. You'd also get scored for smaller things, like popping bubbles, hitting birds, etc.
Also, both games feature a 'running late' feature, that would make stages more dangerous if you took longer. In Ice Climber it's the polar bear, shoving the stage around and causing you to die if you're down too low. In Balloon Fight it's the electric storm, sending one-hit kill sparks flying around the stage.
I think the same group may have made both games, also...
But suffice to say, they're both very fun.