The original Godzilla was a big hit, and Toho Studios wasted little time (less than six months) getting a sequel out. The logic behind bringing Godzilla back from the dead is handled with a reasonable amount of believability, considering we're talking giant monsters here. Turns out the H-bomb tests that awoke the first Godzilla managed to bring more back to life. So in this movie, we get a second Godzilla, along with Anguirus, a quadrupedal monster who gets the privilege of being the first monster to fight Godzilla (in the original film, Godzilla was the only monster). Their battles are OK, given the limitations of having two guys in suits pretending to be monsters. Godzilla dispatches Anguirus, although not before much of Osaka is destroyed. The subtext of Japan being destroyed due to the detritus of nuclear bombs is less clearly a metaphor for Hiroshima and Nagasaki ... there is no explicit anti-American sentiment.
There isn't anything to make Godzilla Raids Again into a classic, but compared to some of the later entries that emphasized kids, it's a tolerable time-waster. There is some silly humorous banter a few times, but mostly, you get two monsters fighting, a city destroyed, and then a novel way to kill off Godzilla once again (this time it involves an avalanche).
The Americanized version was bizarre, as might be expected. It was dubbed instead of subtitled (the version I watched now was subtitled and from the Criterion Collection), with constant narration. For reasons that are not clear, Godzilla is named Gigantis, and the movie is titled Gigantis, the Fire Monster. The American version wasn't released until 1959, on a double bill with Teenagers from Outer Space.