Contested Sequel: Being the first direct sequel of the series, the film has mixed views. Many feel that it's lost most of the atmosphere of the original film. It's still a horror film, but it doesn't possess the amount of tragedy and consequences of the original film, whereas the original has struck a lot of anvils that needed to be dropped. Others enjoy the film for having more Godzilla, more sets to show off and wreck, and doing something new by pitting Godzilla against another monster rather than just have him fight the humans. The series would continue on with King Kong vs. Godzilla as a Surprisingly Improved Sequel/Even Better Sequel
Critical Research Failure: The whole "Origin of Gigantis with stock-footage-laden" makes no sense even after granting license for "giant fire/radiation breathing monsters".
Macekre: Seriously, who wrote the English version? Obviously, the Japanese screenwriters didn't when they wrote the Japanese version. While Paul Schreibman gave the excuse that changing Godzilla's name to Gigantis was to avoid confusion, the English script was ridiculously bad. It's hilarious. Due to his 1999 interview, he said the original title was "Angurus". Yes, "ゴジラの逆襲" (Godzilla's Counterattack) is called "Angurus". The only positive line in the film was "It was the sight to crush the hearts of men" delivered by English Tsukioka (Keye Luke).
Special Effect Failure: The prop used for overhead shots of Godzilla on the island simply stands still without even a budge. It was originally supposed to walk, but either it wouldn't work, or Tsuburaya simply thought it wasn't convincing enough.
Rather than the standard Overcrank in kaiju films that exposes more frames per second and creates a "slow-motion" effect that gives the impression of great mass, Director Motoyoshi took the unorthodox approach of having the cameraman undercrank the monster footage, creating an effect that comes in somewhere between pseudo-Stop Motion and The Keystone Kops. There's a reason western viewers may start hearing Yakety Sax in their heads during the monster fights.
While the JSDF is using their missile trucks to shoot at Godzilla, you can tell the people are dolls on the trucks.
The Godzilla puppet used for closeups is heavily Off-Model compared to the suit, and the frantic jerking-around at times reveals part of the puppeteer's arm.
So Bad, It's Good: The Gigantis cut to an extent. If one found the Japanese version boring to begin with, the hysterical cartoony dubbing and the out of place stock footage are sure to correct that.