Continuity mistake: It's shown in many scenes that the robot Gallaxar sends isn't particularly quick moving when it walks. But when it's chasing Ginormica around the city, even though Ginormica is sprinting away, it can catch her far more quickly than its speed would allow. It doesn't suddenly speed up - in the shots when the camera focuses on the robot again, you can still see it moving slowly.GalahadFairlight
Plot hole: When the asteroid first approaches Earth it does so very quickly, but then it takes hours to finally enter the atmosphere and land on Susan.
Other mistake: When Derek does his final news report the map in the background says both 32 and 99° in Nevada.