It certainly only caters for its target audience, though 'Monster Island' has its moments and I'm sure the young generation will like it.
The animation is the weakest part to this though, which isn't a good sign in this genre. It's very low budget, on the same level as the type you'd see in old video games. Some of the static bits are alright, but all the live stuff (weather, effects etc.) look pretty terrible. The most interesting character is Johnny Rose's Norcutt, despite his under-developed motives.
Away from that though, it's an OK film. The voice cast are acceptable, while the humour is probably pretty spot on for those it's aimed for. I will say though, there is one scene which actually did make me chuckle; it involves Jessie J's 'Bang Bang' song playing over it.
All in all a fairly poor film, mainly down to the questionable animation, but I reckon the intended age bracket will somewhat enjoy.