The fact that, despite it all, the Abbots managed to survive for over a year, even with the monsters lurking out of the view.
When she goes into labor, Evelyn not only manages to avoid screaming, until the fireworks are set off, but there's the fact that she gave birth with no assistance.
Even better, when her water breaks, and after stepping on a nail, Evelyn manages to distract one of the monsters with a timer and runs into the bathroom to give birth.
Lee attacking a monster with an axe. While it led to him getting injured it shows how fearless he is.
There's also his heroic sacrifice which while also heartbreaking shows that he'll do whatever he can to protect his children even if it kills him. He doesn't even flinch when the monster lunges at him.
The end of the film? Who didn't cheer internally when Regan and Evelyn work together to completely disable one of the creatures and Evelyn blows its head off with a shotgun?
Even better? After taking the creature out Evelyn and Regan look at the monitors to see two more aliens come for them. What do they do? Regan grabs the speakerphone and cranks the volume up even louder, while Evelyn loads her gun with a smirk! The Abbot family is ready to fight back!
The film fully employing Disabled Character, Disabled Actor, subtitles, and little music, instead of the usual Hollywood pitfalls of casting hearing people in Deaf roles and using simplified sign language.
The creature design itself. After tons of Alien knockoffs and derivative, cliched designs, it's quite refreshing to see a unique and interesting movie monster that manages to be truly alien and frightening (though inevitable comparisons to the Demogorgon abound).
The movie defying Stay in the Kitchen, with Evelyn being a Pregnant Badass and Regan finding out how to defeat the monsters in the first place.
