Considering the fact that the world is ending, it's pretty incredible how focused and zoomed in the film stays. We only get to see the small world of the bunker. There are no broad, sweeping views of giant cities crumbling. We don't see a shot of the gargantuan alien army descending from space. That takes restraint, and it pays off. It's kind of like the first Cloverfield: sure, there's a giant monster attacking the city, but we're almost too wrapped up in the protagonist's mission to find and save his ex-girlfriend to care.
It remedies a greater problem with many of these large-scale action movies. There are thousands and thousands of casualties. Death becomes meaningless, inconsequential. When your whole world is an underground bunker with three characters, though, it matters. That's what makes the story compelling. That's what makes the idea of loss monumental. It makes for great, powerful storytelling.
