I think all of us could go on for days on this one.
One point to note is how skillful older films were at creating an impression back before computers could put anything you wanted on film easily.
Look at your example from "The Thing." That required a plywood fin, and some creativity. Later versions, of course, would show the saucer in loving detail.
Look at how Spielberg handled the shark in "Jaws" before it actually made an appearance. It was damn HARD to have that shark make an appearance, and creativity was required.
Horror movies used to rely on implication a lot more than visible gore.