I havent had the opportunity to try it yet but I heard from my music teacher thats its pretty good. Basically you learn the real notes of songs. When you play at easy level they wont make you play all the notes. When you go on higher levels, you play all the notes from the song.
He also told me that there's a tiny lag between what you play and what comes out from the speaker in the game. But maybe there's some way to fix this.

Since you play with your reel guitar, it works out your fingers like you would when you play "for reel". But my concern with the game is that you will learn the song note for note by heart without learning the music theory behind it and that's a key factor in our growth as musicians. Its cool to play a song we like but when it will come to improvisation/jamming over the song, you wont know what to do (unless you have a good ear and can figure everything out just by listening).

I'm thinking of buying it since I have a little boy that will enjoy this game a lot. At the end of the day, theres no right or wrong. If it makes you play more and enjoy music more, its good :)