Amazing...well for that age
Answer number one THE REVOLUTION
Before Excitebike, every game of Nintendo was Mario or an anamorphic boy, a car or in the best case an animal or a plane. In excitebike, you was an anamorphic boy but you was on a Motorcycle and yo can Break your neck in those cool spins and make a lot of things to be the best of the best.
Answer number two MULTIPLAYER
This game turn on your Killer instincs in a great multiplayer option an that was so fun because you was "killing" your brothers or friends in a great race and anithing is better than look at your partner face when you kick her ass in first place.
Answer number three CONSTRUCTION POWER!
I always hate a game who don't let me make my own scenary (and a lot of games don't have that option) but Excitebike let me be got in the game and make my own pit. That was so cool
Any other answer, please ... let me know