If you like the Japanese Godzilla movies of the 60s and {especially}the 70s made by Toho Studios, than you're probably like this effort, a not totally successful but fun attempt by Shockiku Studios to get in on the act.
King Kong obviously inspired the early section of the film,but oddly enough the film mostly bases it's plot on the British 1961 monster movie Gorgo {itself a Godzilla imitation},with a baby monster captured by humans and it's angry parent wrecking havoc to get him back. However,unlike Gorgo's one vengeful parent,here we have both mum and dad monsters attacking poor Japan {one wonders why anyone still bothers to live there in these films,since it's always being destroyed by giant monster year after year}.
The film lacks the polish of the Toho films,with the miniatures lacking in detail and some rather drab photography and poor editing. Music is mediocre although the two songs {only in the subtitled version}are memorable for the wrong reasons. However,the family Gappa are uniquely weird monsters,the action is pretty continuous after the first half an hour and the final reunion scene involving the monsters is touching. There are some amusing touches which gently mock the genre. Feminists be warned though-the end scene where the human heroine realises her role in life will probably offend you greatly!
Hardly a classic of monster movies but silly and entertaining anyway. A good one to introduce young kids to the genre.