"Monster Island" as a concept showed promise.Regrettably, the writers seemed to have no idea, what to do with this 1950's style, retro monster story.
This film wanders around aimlessly, for the majority of its run time. What it should have done, is quickly establish a survivalist tale, where the underdog protagonists, take a range of risks and set traps, to defeat the vicious humanoid amphibian creatures, stalking them.
In summary, strong casting choices, plus a great retro concept, that could have worked so well, had the script had a clear purpose and direction. As its stands, a mediocre watch.