Plot hole: When the robot pilots first connect after the first attack, Red tells the story of his battle. They don't seem to even notice the dozen or so civilian bodies they have to actually physically step over - and the bodies are just lying there along the sidewalk & parking lot; no signs of any monster attack, so how did they die?
Factual error: At the start of the movie, the oil rig discovers the first monster. The characters reference the seabed there being at 800 fathoms - which is pretty deep; they'd have to be hundreds of miles or so offshore for the ocean to be that deep. However, the oil rig is just a few miles off a coastline, as the background view shows.