Mature themes, but good.
Cons: The plot was not as fluid as it could have been. While the handling of certain mature themes were scripted well, the pacing was hurried and left you no time to absorb what the characters were going through. The backstories of the main characters also seemed thrown in for convenience rather than syncing up with the narrative. Animation and action sequences were unbelievable/unrealistic at times where it was distracting.
Pro/Con: Death/loss, animal cruelty, action heavy, ambiguous villain. Happy ending is both satisfying and unsatisfying.
Pros: Handling of mature subjects: Loss of a loved one, facing the lies our parents tell us to protect our feelings, and discovering the truth and its consequences. The point of these themes were put across clearly in few words and without becoming lost in the action. They were also shown from three different points of view: the child, the parent, and the elder/supporting characters.
Overall: A fairly good adventure movie. I would rate it higher if the plot was more streamlined, but for a kids movie the pacing is standard and the action is fun.