Film The Nagasaki to Gojira's Hiroshima
Sequels are generally considered to be inferior to the original. However, with a work of art like the original Gojira setting the bar really high, it's not hard to see how its sequel, Godzilla Raids Again, falls somewhat short in comparison. That's not to say that it's not good in its own right, though. For a movie that would kickstart the "Godzilla Vs. another monster" trend, Godzilla Raids Again is a decent flick that, while nowhere near as good as the original, is a fun movie that will appeal to anyone who enjoys giant monster movies.
The american edit, Gigantis: The Fire Monster, is more or less the kind of movie that would be selected for riffing by the Mystery Science Theater 3000 crew. It makes an attempt to be something different than what it originally was, but the result is probably one of the worse U.S. edits made to a Godzilla movie. However, it does have some positives. The rather cheesy dubbing can be funny at times, and the music, while no substitute for the original, does improve some scenes quite a bit (an example would be the action movie-esque scene with the criminals escaping from the van, a scene that originally had no music in the japanese version).
Classic Media released the movie on DVD, including both the original japanese version (with english subtitles, of course) and the american version onto a single disc. It also includes commentary that was done by Steve Ryfle and a few other commentators and plays over the american version. Said commentary talks about not only the american version and its changes, but also the japanese version and how it compares to the original. I highly recommend Classic Media's DVD release to anyone who wants to own this movie.
Film I enjoy Gigantis/Raids Again
First off, I am well aware of the public opinion on Gigantis, and Godzilla Raids Again in general.
I love this film, despite how bad, hilariously and otherwise, it is. Anguirus is actually pretty damn terrifying in this film, as is Godzilla. [1]◊ [2]◊
The way they portray the monsters' fight is brutal, and isn't seen again in the rest of the Showa era, with Godzilla killing Anguirus in a fashion unrivaled since.
In Gigantis, changing many of Godzilla's roars to Anguirus' actually WORKS. There is one scene where "Gigantis" comes out of the water, and Anguirus' roar is heard. That scene is made more effectively creepy because of it, and is one of the reasons I watch Gigantis more than Raids Again.
I enjoy both versions greatly, and the film itself ranks high on my list.