I've noticed that when he's happy there isn't much going on when compared to the other two emotions. Something to think about.
You probably wanted to test just the three emotions, but seeing as how this went so well you should do more. Make a greater range of emotion and do a bit more with the backgrounds. I like that the backgrounds are affected by the emotions they correspond with. They could use some work though. Try a themed background. Maybe drawing some objects that sync up with both the emotion and the color background you choose. For example, you could have falling mint candies to go with the happy background. (If you like mint that is.)
Keep going at it.