The second film on my kaiju marathon is Godzilla Raids Again sometimes better-known in the West (if it's known at all) as Gigantis, the Fire Monster. The second Godzilla movie and the first to feature another kaiju besides the King of the Monsters himself Godzilla Raids Again is an important landmark in Toho history, even if it is no one's particular favorite.
After the box office success of Godzilla in 1954 Toho was eager to capitalize on the film's success with a sequel. As a result, Godzilla Raids Again was pushed into production before the year was out and was released less than six months after the original. Considering how rushed the film was and the fact that Ishiro Honda declined the director's chair, it's surprising Godzilla's second venture turned out as well as it did.
In comparison to the original film Godzilla Raids Again is a more personalistic film, with much of the film's focus on two characters in particular: Koji Kobayashi and Shoichi Tsukioka, both pilots working for a shipping company based out of Osaka. Whereas Godzilla changed perspective between several characters who were loosely connected to another with relative quickness, Godzilla Raids Again is told mostly from these two characters' perspectives as well as Tsukioka's fiance Hidemi to a lesser extent. It is through their eyes that we witness the appearance of this new, second Godzilla (for it is indeed stated unequivocally that the original was killed by Serizawa) as well as the destruction it wreaks on Osaka.
In some ways this grounds the film a bit more and gives it a bit of a personal touch that Godzilla sometimes lacked; the romance between Tsukioka and Hidemi is more believable here than Emiko and Ogata's affair was in the 1954 film. Neither though is an exceptional case and the minor subplot surrounding Kobayashi's search for a wife of his own feels somewhat out of place, which may account for its removal from the American version of the film. All in all, whether one prefers this approach or the pseudo-documentarian style of the original Godzilla is largely subjective.
One of the main ways in which this film distinguishes itself from the original Godzilla is that it is the first kaiju film to feature more than one monster and to pit them against one another, something that would become increasingly common over the years. Godzilla's primary adversary in this film is Anguirus, rendered here as Angilas (which is technically a better romanization), a mutated ankylosaurid of similar size and power to Godzilla (sans the King of Monsters' radioactive breath). The kaiju fights here are interesting, to a large degree because, compared with later battles in the series, they appear far less choreographed and much more similar to actual animal fights. The frame rate for the fights is also noticeably sped up, likely to compensate for the difficulty the actors experienced fighting in the giant rubber suits.
Like Godzilla, Godzilla Raids Again was significantly changed during its localization in the United States. However, whereas Godzilla, King of the Monsters has experienced some popularity and is even generally well-respected within Japan (where it was released in 1957 as an updated version of Godzilla), Gigantis, the Fire Monster is generally looked down upon by modern fans. This may be in no small part due to Warner Bros' rather odd decision to try and frame the film as an entirely original production, unrelated to the original 1954 film. Godzilla was renamed Gigantis (and given Anguirus' roar), all references to the 1954 film curtailed, and both Godzilla and Anguirus were declared to be "fire monsters" rather than dinosaurs mutated by nuclear testing. The only highlight from the production was that it provided an early career boost for George Takei, who'd later acquire fame as Hikaru Sulu in Star Trek as well as a major LGBT rights activist.
On reflection, I actually enjoyed Godzilla Raids Again quite a bit. It has its weaknesses: the aforementioned Kobayashi subplot, the somewhat lackluster climax, and an underwhelming soundtrack by Masaru Sato (better known for his collaborations with Akira Kurosawa), but on the whole it's a fairly good follow-up to Godzilla and sadly underrated both in America and Japan. It's not as dark as the first Godzilla or some of the later Heisei films and it doesn't have the whimsy and fun of the later Showa films but it tells a decent story and sets several important precedents for the series down the road. As such, I can definitely give it a thumb's up.