Some people have commented on the seemingly heavy-handed politics of Monsters - the issue of border-crossing and the Wall and of course, Mexico being an "infected zone" that must be kept at bay - and the most awkward lines of dialogue are the ones that try to straight-forwardly discuss the idea of America building walls and sealing itself in, and how different America looks from the other side of the Wall, and we "forget all this" when we're in our "perfect suburban homes." But that's extraneous stuff that's not at the heart of the movie. Monsters goes beyond any current political issue. It's really about coexistence/extinction/evolution, and the possibility of understanding an alien that isn't a humanoid little big-eyed bugger but looks like Cthulhu.
Serious kudos to the decision not to make these aliens totally horrific, by the way. They do kill people, but for them it must be like swatting at flies, and they do other things besides kill - they hang out in lakes with fallen aircraft, they moan plaintively, they lay their pretty glowing eggs in trees that the U.S. military then chemical-bombs, they turn off televisions, they communicate with each other through gentle touch and look like ethereal, celestial beings.
It's sad that people have said nothing happens in this movie - I'm guessing because aliens aren't popping out every other minute and having fist fights with the main characters - because the movie shows that a great deal has happened since the alien-carrying space probe landed in Mexico and North America is continuing to change. It's a bottom-up movie, which means we don't see the U.S. president frowning over the situation with his cabinet, and we don't see people living in underground shelters or totally extinguished or anything - because this is about how life went on in Mexico after the aliens landed. One of my favorite bits was a five-second clip of a Mexican info-cartoon for children showing a happy little Dora-the-Explorer-like girl putting on a gas mask and standing in front of a wall, behind which a googly-eyed, unthreatening squid monster dances around. Those kinds of details make Monsters remarkable.
A Mexican port official explains that if you have money, you take the ferry to the U.S., bypassing the alien-infested infected zone, and if you don't have money, then you "go by land." Third-world-first-world relations continue pretty much as they always have, with passport drama and bribe drama and "why do your friends have guns" drama, as an industry of illegal infected-zone crossing has developed. In a lot of ways Monsters is more of an "Americans trapped outside America!" movie, but it's a Grade A example of that subgenre, neither making things unrealistically easy or unrealistically hard, and not making it about Evil Dangerous Mexicans threatening the Poor Innocent Americans. But then there are moments where the movie rises above that subgenre - when the leads find an ancient pyramid that's been grown over by jungle, for example, leading you to wonder if our civilization will also be overtaken by these new lifeforms. But who can say? What little we see of the U.S. implies that the American people have an inflated, confused perception of the aliens' threat level, because they don't have to deal with the aliens on a daily basis. But the people of Mexico have been living within spitting range of the infected zone for six years now (the wall protecting the U.S. from the infected zone is made of brick, and the one protecting Mexico from the infected zone is more like a very tall fence), and they're not going to leave because their work is here, their family is here, as a taxi driver explains. They've also started to pick up some things about the aliens' life cycle and behavioral patterns, and the aforementioned friends with guns explain that if you leave them alone, they'll leave you alone - this doesn't quite work out because there's so little bridge of understanding between the "creatures" and the humans, but these scenes of altered, adjusted life - after the running and screaming is over, as the director says - is really what I watch sci-fi for, and Monsters hits this out of the park. I bought this world. Detailed, believable, and intense. Nothing like the ridiculousness of Avatar.
Also sad are the comments I've read saying this is just a relationship movie. I don't even know what to make of those comments, honestly. So many sci fi movies feature heroes with love interests, but I doubt anyone said that Transformers was a relationship drama. The two leads develop a bond that can't be consummated, because she's engaged. Is it because they have actual conversations and think about their lives? It's not as if the action stops so that they can stare into each other's eyes. It's baffling to me that anyone could think there was too much relationship drama, but sort of reminds me of a couple discussions in SF/F lately about how if you include a sex scene or too much relationship stuff then a book somehow jumps out of SF/F and becomes romance - yet another "issue" that I cannot wrap my head around (does that mean Updike wrote romance? it's laughable, the obsession with formulas that some SF/F fans have).