Gamera may tower over Japanese cities, but he is a huge monster... turtle. Sure, he has a flame breath weapon and some strange leg and arm jets that allow him to fly like a flying saucer, but when one of his recurring defensive moves is to pull his head into his shell to avoid an incoming attack, the comedy begins to creep in. Sure, that gag was done once or twice in Teenage Mutant Ninja Turtles, but those were supposed to be funny; it's very hard to tell which parts, if any, of Gamera are supposed to be funny and which parts are unintentionally funny.
Gamera vs. Zigra / Gamera: The Super Monster Double-Feature Collector's Edition, as the name implies, features two Gamera films. The first one, Gamera Vs. Zigra pits our hero, Gamera, who is evidently a sworn friend to all children, against an aquatic alien usurper who seeks to enslave and eat the worlds' land-dwelling population. I don't speak Japanese, but from the English dubbed version, I learned that Zigra, from the planet Zigra, evidently had to leave his planet Zigra, because the planet's oceans became polluted and destroyed by Earth technologies (no explanation was given for that), forcing Zigra to search the galaxies for a new planet with clean, livable oceans in which to live, so when he found Earth with its nearly destroyed oceans, he decided to move here, in our nearly destroyed oceans because we didn't deserve them. He would take over the Earth and show his might to "all of the other planets in the world." No, I don't really know what that means either, but it is a good example of how confusingly and mind-numbingly bad the Engrish-dubbing can get.
Gamera vs. Zigra has several strange English translation flubs, some laughable special effects and props and some scenes that will leave you confused, at best, but it does manage to be very preachy about humans' responsibility to protect the Earth's oceans and what a bad job we've done to date. Gamera: The Super Monster, on the other hand, is truly a head scratcher. The entire movie is what television series typically refer to as a "clip" episode. There is a new storyline which involves people who never actually interact with Gamera, and when their story leads them close to Gamera, a fight scene occurs between Gamera and one of his enemies from a previous Gamera movie. In fact, if your main interest in this type of movie is the fight scenes, then Gamera: The Super Monster is the movie for you, as it has several abbreviated, condensed fight scenes from various previous movies. You could think of it as a sampler plate of Gamera films. However, the storyline, itself, is uninspired and really goes nowhere. The first half of the movie or so has a space pirate in what looks litigiously close to a Star Destroyer from Star Wars on his way to wreak havoc and destruction on the Earth, but has his agent sent ahead to remove any resistance. This resistance primarily takes the form of three "Space Girls" who have pledged to protect the Earth and not to use weapons or unnecessarily hurt people. Unfortunately, the Star Destroyer has the ability to shoot the Space Girls from quite some distance, if they transform, Macarena-style, into their super-powered forms. This leads them to call upon Gamera who fights off various super monsters released on the planet, without ever being able to really do much of anything to intervene. If the plot sounds a bit weak, you're giving it too much credit. About two-thirds of the way through, the story basically gives up and stops following Gamera, but we still cut back to Gamera fights from time to time.
Both movies offer a lot of chances to laugh, as there are quite a few scenes that look like they could have been made in a high-school film class. I'm probably not the intended audience for these movies, as I can't really understand a cult following for them, but I did find several parts laughable, and enjoyed several of the "I can't believe they just did that" and "Really? I could do better with my phone" moments. The video quality is grainy in places, mainly in the stock footage, some of which appears to have been taken during WWII. There are places in the soundtrack where I could hear the sound of film clicking over the sprocket of a projector. The special effect of a van transforming into... an orange, um, circle of light is especially laughable, but the inclusion of cartoon images of a train in space with Gamera superimposed is beyond the pale.
If you're looking for cinematic history, I would advise something else. If you're a nostalgic fan of Gamera, my only warning would be that the Gamera vs. Zigra / Gamera: The Super Monster Double-Feature Collector's Edition isn't really that big on "Collector's Edition," coming up pretty short in the special features department. If you like these old-school special effects that are string-heavy and you don't have a problem with monsters being represented by models, pictures and men in suits, at different times... where all three are quite obvious, then you may enjoy these movies quite a bit. Personally, I enjoyed the laughs, but don't see myself watching them again, or, for that matter, seeking out other Gamera movies... I mean, hey - I've already seen several of the fight scenes, right?