It was fun, I'll give you that. I had a hard time getting used to the controls, and most of the time the sound came out a little later than when I pressed a button on the keyboard, which messed up my playing. What bothered me about this game is the amount of time it took to go back to the main screen after losing, or to move on to another song. I got impatient at one point and stopped playing because of that. Also, it would've been best if you started with an easy song, and then increased the difficulty throughout the "levels". The songs that I managed to play before losing all had (or felt like they had) they same level of difficulty.
Overall, despite the criticism, I enjoyed the game. Free play is a fun option.