I bought the piano wizard premiere for my DD as a Christmas present. Keep in mind she is only 2 so I don't expect she will have a full ability at this age. I choose the premiere b/c you are not limited to the songs they provide. You can download anything and the program converts it so they can play.
I have mixed opinions on it. The video game strategy is brilliant and even with a two year old she is able to 'get' the concept of when to push the key and what color key to push. My problem is I don't like the additional background music that is played for the song. I would rather it be completely them playing to produce the music. But this is level one and perhaps by level 4 the background music goes away. I will look at it and let you know. Overall, I am happy with the purchase and she loves it. She doesn't play it everyday but when she is in the mood it is there for her and she will play for a good hour which is amazing at this age.
If your son is into video games or even the wii rockstar or guitar hero games then the piano wizard will be right up his alley. It will be something he won't feel pressure doing and it will be fun. That alone might encourage him to give the piano another try.