These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Awesome Music: The soundtrack made by Jon Hopkins is absolutely beautiful to listen to, especially the main theme.
Crowning Moment of Heartwarming: Andrew and Samantha spend a single night with a hospitable family after leaving the train at the start, where Andrew was so good with the children that the mother wondered if the pair were married. When they leave, she offers them food and water and gives Samantha a goodbye hug.
And while alluded to prior to their trip into the Zone, their conversation with the smugglers strongly implies that the American government's bombing of the creatures is what's causing hostilities, rather than the other way around.
Visual Effects of Awesome: Considering the tiny budget, anything resembling special effects would have been commendable but its visuals would actually shame some movies 100 times its cost. And Gareth Edwards did it all himself. Special mention goes to the ending, when two of the creatures meet whilst Samantha and Andrew look on in awe.
What an Idiot: Andrew's admittedly drunken decision to sleep with a random woman simply because Samantha shot him down isn't so bad considering he's single. She probably only rejected him due to fact he was so drunk or maybe conflicted over being still technically engaged. But the true error of judgement comes the morning after when his fling ends up stealing Samantha's passport and Andrews cash. Leaving your valuables unattended with your room door wide open is a bad idea in general. Moreso with a stranger still in your bed.
A bit onto Sam, too, for leaving her passport with Andrew who she technically didn't have to see again before getting on the ferry, alongside the fact that she stormed off in a huff while leaving said passport behind.
What Do You Mean, It's Not Political?: The director has denied parallels with Mexican immigration to the United States, but a lot of people have still drawn the comparison. The fact that Mexican immigrants making the border crossing are characters within the story and there really is a wall being built on the Mexican-American border does not help.