Pretty simple game, but well executed. The changing mechanics set a nice pacing to the game, and the art is pretty cute.
Perhaps lack a feedback to tell when the character will change emotion, perhaps on the emotion FX itself (like the flame getting less strong when approaching the change for example.
Also, the rainbow mode is cool to go crazy, but intuitively I didn't think about rushing into the books while in this mode, perhaps just because the visual for this emotion doesn't look very "aggressive".