It's infinitely charming and very unique.
That said, you can do all there is to do in less than an hour, easily. And sadly, Nintendo could have used the game as a chance to really step up the replay value by allowing you to save your generated music, and then perhaps gone even further by allowing you to share it with others.
As it stands - which is little more than an interactive proof of concept - Electroplankton is very neat. But given the sheer shallowness of it, most people will not be happy with it if they paid a large sum.
Me? I personally love it. It's soothing and I love to take it out occasionally and set it to audience mode. But I'm strange and wear the human pants.