These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Horror: All cars fly, and all buildings are miles above the ground, standing on stilts. The ground is rarely, if ever, actually shown. It's been theorized that maybe the world flooded, or went through some environmental disaster. (A Harvey Birdman episode joked that they lived so high up because the ice caps had melted and flooded the earth.)
Actually, in the original 1960's series, ground level was shown on a few occasions and it was perfectly fine, with trees and grassy hills. The whole idea of an uninhabitable Earth's surface in The Jetsons came in the 1980's revival, when the Green Aesop trope was popular, so the 1990 movie shows people all living above a thick layer of pollution.
But then, humans might be staying off most of the actual ground level in order to let it recover. The few decent areas are probably under National Park service.
Jane does take a vacation shown to be on ground-level Earth, specifically the western US.
Fridge Logic: Why are Elroy and Judy blondes when their parents are both redheads?
Most probably both George and Jane possessed a recessive blond trait in their genes. (It would have to be really recessive, though, considering that red hair is itself a recessive trait)
Either/both Jane and/or Judy could be playing around with hair dye.
Or Judy and Elroy could be made-to-order genetically altered children.
Considering the fact that the cars fly miles in the air (and according to the 1990 movie can get stuck in traffic), what happens if the car runs out of fuel while it's in midair.
Pretty harsh one in the second season: the family is watching TV one night and learn that the priest who married George and Jane was actually a con-man, and that this one thing somehow meant they were never actually married. This means Judy and Elroy are bastard children. How did this episode get green lit?
Harsher in Hindsight: The moving sidewalks stick out in the actual twenty-first century (though mostly seen in airports), where most people these days are becoming fatter and lazier due to poor diet and little to no exercise.
Dying Moment of Awesome: A real life example as both George O'Hanlon (the voice of George) and Mel Blanc (the voice of Mr. Spacely) were both near the end of their lives making this the final movie of their careers. This is especially noticeable with George O'Hanlon who was getting so weak during the end of production that he could barely record his lines, but refused to give up before he finished this movie.
They are, however, close friends of the building's superintendent, Henry Orbit. Maybe he gave permission to Rosie (his robot assistant's girlfriend) to raise and lower the building?
In any case, this previously happened in a 1960s episode, where the building rose above a storm.
Moral Event Horizon: You know those innocent Grungies being killed by Spacely's drills? He knew they were there and he started drilling anyway, and he fought to keep drilling until George shut the drill down via pinpoint sabotage.
Tear Jerker: When Elroy nearly dies, and George and Jane's reactions after he is saved.
A real life example with both George O'Hanlon (the voice of George) and Mel Blanc (the voice of Mr. Spacely) who both died shortly after recording their lines and never got to see the finished product.
Visual Effects of Awesome: The CGI used in the movie. Of course, the effects are dated nowadays, but back in 1990, these computer animated scenes were amazing.