Note: Star ratings are based on both the included Japanese and US versions combined.
The story behind the creation of the Japanese produced Frankenstein vs. Baragon (called Frankenstein Conquers the World in its American release) is far more entertaining than the film itself. Released in 1965, the story dates back to the original King Kong. It's a shame the film's rather lackadaisical pacing doesn't follow the behind-the-scenes story.
After King Kong's success, special effects master Willis O'Brien (the man who animated the great ape) had the idea to resurrect the creature for a new sequel sometime in the 1960's. It was to be called King Kong vs. Prometheus, the new creature being a spin-off Frankenstein's monster. After Jon Beck, a Universal studios employee, got a hold of the script (which was rejected by numerous other studios), he took it to Japan.
O'Brien passed on in late 1962, but only after learning the Japanese turned the script into King Kong vs. Godzilla, released the same year as his death. Ever crafty, Toho Studios still had the original script and idea. In 1965, it became Frankenstein vs. Baragon.
The concept was radically altered, turning it into one of the oddest Toho giant monster films, and given their general premises, that's saying something. Frankenstein's "immortal" heart (from what film is never known) is transported to Japan for study during World War II. Exposed to the Hiroshima bomb, it turns into a deformed human with some of the more familiar Frankenstein trademarks (scars, flat head) 15 years later.
Brought in for study, the human/monster hybrid grows upon the radiation rapidly, though why he stayed around six feet tall for 15 years prior is never given an explanation. This also leads to the appearance of Baragon, a four-legged subterranean monster with glowing horned nose. In standard Toho logic, the monster appears only as Frankenstein grows large enough to fight it.
Incomprehensible as all of that is, there's still some fine work here from a recognizable crew. Ishiro Honda directs as he would most of the Toho monster output of the period. Eiji Tsuburaya provides the overly large miniatures (necessary because of Frankenstein's smaller than typical height), some of the best of his career. The final piece, aside from the standard acting staple (in addition to The Rebel's Nick Adams), Akira Ifukube provides a rousing soundtrack, though some of the pieces were culled from 1962's flop Varan The Unbelievable.
The film relies largely on the human drama to carry itself, including a relationship between the giant and lovely Kumi Mizuno. It drags along through generic research where the scientists deal with the monsters regenerating powers, the moral consequence of killing him, and the media's appetite for whatever information they have. Excessive stretches are wasted on meaningless conversations that have little bearing on the overall plot.