...turns out to be a modestly inventive and involving variation on a standard-issue sci-fi doomsday scenario.
—Joe Leydon Variety
Capable and compelling performers like Hirsch and Thirlby seem left to their own devices to make some connection with the material. The idea of semi-invisible aliens, an unseen enemy, should mean the film has a lingering sense of paranoid abstraction (not unlike "Right at Your Door"), but Darkest Hour never gets beyond rote efficiency.
—Mark Olsen Los Angeles Times
—John DeFore Hollywood Reporter
You should be rooting for the humans, but you might as well be rooting for the blobs. Most likely, though, you'll just be rooting for the credits.
—Keith Staskiewicz Entertainment Weekly
Really, how slovenly is it to use invisible aliens? If you're going to tease us with nothing but pinwheels of light for three-quarters of the film, you'd better have one heck of a reveal up your sleeve.
—Jeannette Catsoulis New York Times
Not since Mark Wahlberg trembled in fear beside a menacing houseplant in The Happening has a film tried to provoke terror with such an unlikely object of menace.
—Nathan Rabin Onion AV Club
In a year-end season stacked deep with worthwhile films, what possible incentive could there be for submitting to The Darkest Hour's utter pointlessness?
—Budd Wilkins Slant Magazine