I was really tempted to give this film a Qualified Recommendation. Not because it's in any way good, you understand. Because it is really, really, really, really not. What it is, however, is so deliriously, dippily dreadful that it kind of infects you with a Cinematic Stockholm Syndrome and you - well, I - like it despite its complete absence of anything resembling quality.
I'm not going to bother you with the plot since it is (a) the usual 'aliens want to take over the world and Gamera stops them' thing we've seen before and (b) flagrantly an excuse to re-use footage. About 1/3 of the run time, and 98% of the scenes that actually involve Gamera, is recycled footage from the old films. Instead, I'm going to share with you the dreadful joy of some images from the film.
Such as the opening shot.
I dub thee the USS It's Totally Not A Star Destroyer, Honest
Yes, this is really in the film
Or pretty much anything to do with the good guy "Space Women" who help Gamera fight the bad guys.
"Help" may be exaggerating their contribution
Actually, you know what? Have a trailer. It's in Japanese, but it won't matter.