"No One Will Save You" never quite follows up its breathtaking opening act in similarly masterful ways and ultimately indulges in some overly elaborate creature designs and theatrical set pieces that suck some of the tension out of its protagonists ordeal, but it still manages to be one of the best alien abduction horror movies in a good while. In a nearly wordless performance that calls on her acting chops to react to the incredible forces working against her character's safety and sanity, Kaitlyn Dever turns in a fantastic performance as Brynn, ably carrying Brian Duffield's film through its murkier patches and enhancing its high points. A savvy, already traumatized protagonist, Brynn is a great anchor for the story, and Duffield does a decent job of intertwining her past with her present circumstances in palpable, even slyly humorous ways. (That ending will probably turn some people off, but I liked it.)
The best thing about "No One Will Save You" is that it's actually scary, which is a rarity for modern sci-fi/horror (in my opinion, of course). I would have preferred it to have been a little more pared-down and classical in its depiction of its aliens and their abduction scheme, but I'm still grateful for its overall effectiveness. And I'll always sing the praises of that awesome opening act.