There’s nothing like a really bad Japanese monster movie, and Destroy All Planets is a a really really really bad Japanese monster movie! It has all the ingredients you expect - irritating boy genius children, amazingly bad special effects, a script that relies on the bad guys doing unbelievably stupid things, and the destruction of Tokyo (which I don’t count as a spoiler since it’s not a Japanese monster movie if Tokyo doesn’t get destroyed). It also has flashbacks to previous adventures of Gammera, to pad out the running time.
And it has Gammera himself - the most delightfully weird of all giant fire-breathing flying turtle movie monsters. OK, so it’s the only giant fire-breathing flying turtle movie monster, but it’s still wonderfully bizarre. As a bonus, this one has a terrific Pop Art alien spaceship that looks like it belongs in a 60s discotheque.
Of course there has to a climactic monster-on-monster battle, and this time Gammera is pitted against a creature that looks like an enormous malevolent budgie with tentacles! This evil and ferocious octopus/parrot hybrid certainly provides Gammera with a challenge.
One can only nope that if Earth ever is invaded by aliens, the aliens will be as inept as these guys. Being outsmarted by a couple of annoying Boy Scouts has to be very embarrassing indeed if you’re an evil alien race bent on dominating the universe. Their basic idea - of holding children as hostages and then using their mind control technology to force Gammera to do their bidding - isn’t an entirely bad one, but their execution of this plan is distressingly incompetent.
But of course Destroy All Planets is a 1960s kids’ science fiction movie, so it’s hardly fair to criticise it for being a bit on the sully side. The main thing is - is it entertaining? The answer has to be yes. I’m personally not the biggest fan of this genre of movies, but it has to be admitted that they have a level of delirious insanity that you really don’t get in any other type of movie. That alone is sufficient reason for watching.