This movie was surprisingly philosophical and psychological under the hood, so to speak. The way I see it, it gives some perspective into how to deal with mental and emotional growing pains and how to take control of yourself. Most of the story can be interpreted in a metaphorical way, and the movie isn't obnoxiously difficult to read in that sense. More important than decoding some hidden meaning is the feeling and outlook that the story gives: it should already be quite helpful and basically conveys the same things. In any case, the song playing during the credits will spell it out for you.
The technical and artistic execution is very good. It's an entertaining story, although the end part can be a bit dull if you're not into its philosophical aspect.
I'd recommend The Boy and the Beast as near-mandatory watching for teens and preteens, and I wish this movie was around when I was that age. Truly an excellent film!