Why no Mars?
Frankly I thought this movie was very weak, so maybe the answer is just that it was written by rather incompetent people, but I don't understand why they cut out the Mars angle? It worked in the short story and the original movie.
Although I also think the original movie was vastly superior. I kind of dig that they tried to to be original and different after all. The ideas failed, but kudos for the try.
And frankly, the Mars setting wasn't all that important to the story in the original movie (other than just being an exotic setting) and certainly it was not important in the short story either. Aliens were, but this was almost but entirely skipped too... so, for me we can bash the movie for many other reasons but likely the biggest is that we simply cannot compare the two... and how could we ever?
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** I am normally not a praying man, but if you are up there, please save me Superman **