Does anyone else think of “Invasion of the Body Snatchers”? The first two versions are thoroughly compelling and Donald Sutherland’s role in the '78 remake is really good. The flick is scarier than your average slasher movie IMO, because it’s clear the aliens are winning. No CGI crap to distract from the story.
The only thing missing that would make it a perfect match is that the director, Phil Kaufman is not the same Phil Kaufman who snatched Gram Parsons’ body and set it on fire at Cap Rock.
So if you see a large oozing watermelon thing, squirming on your tarp, bash the jebeezus out of it!