Pros: It's fun. I like that you are able to unlock new songs by successfully playing other songs. It encourages you to practice and keep playing, rather than just buying them. I like the variety of songs, and they aren't so "expensive" that you can't unlock any. The reward system/value is good. You can choose which "channel" to activate when playing, so the difficulty increases if you want to play more notes and chords at once.
Cons: Once you unlock a song, there should be a way to preview it over and over so you know what the song is supposed to sound like or how it should be played. I can't seem to complete Amazing Grace, even the easy version, because I can't get the timing right. I have to complete it in order to earn more points, so I'm stuck without knowing how I'm supposed to really play the song. I can play it fine on real piano, but I can't match the right tempo it wants on here. Also, some of the notes on paper don't match up on the keyboard so it's not completely realistic, but it's still fun.