With a title like "Monsters", and a story that begins with "six years ago NASA launched a probe..." one might think this to be a sci-fi extravaganza with aliens trying to take over the world or something. That aliens may indeed be taking over the world, yet in such a natural and subtle way, is what makes this small budget film work so well.
Who are the real monsters, remains the question. One could certainly argue that it is the good old US of A who, after bringing the organisms to earth (and then crashing the probe into Mexico - how's that for hands across America?) set up a quarantine zone to keep the creatures in check. Of course a bit of forward thinking - something our government seems incapable of - would have humankind either embracing the species - which somehow doesn't seem likely - or removing the "contamination" by whatever means necessary. Spending billions building a wall across the US/Mexican border is, as usual, wrongheaded and, as usual, doesn't work (although it makes a nice allegory to the current immigration issue in the US).
Delving further, one could also look at humanity itself as a monster - as for sure the alien species does come off as rather sympathetic, and for all their alienness, not all that different in their main desire - to exist, and therefore propagate. The film does a really nice job of giving the aliens some very animalistic tendencies, including migratory cycles that the US is aware of, but can't seem to deem as earthly and "just like us". The film's climax aptly draws that parallel ( by including what has to be the most unsexy kiss ever filmed - but perhaps that was the intention... to show that humanity is really just our base instincts and a bunch of rhetoric).
The film also shows us the seedier side of humanity in that we always seem to find a certain type of profiteer who hover around any catastrophe - anxious to make a buck while people suffer.
First time director, and film's writer and effects creator, Gareth Edwards has taken an idea and made a very true film, beautifully filmed, and has the gift of being able to say much by inference, although he is a bit obvious, especially concerning the female lead and her "engagement issues". Really, the interplay between the two main characters (arguably the ONLY characters) isn't all that poignant or dramatic, but works in its own quirky way - in spite of some overzealous acting by the male lead).
Yes, the film isn't perfect, and if you were expecting War of The Worlds, well it's not that type of film (thank goodness), but rather a fine expose that allows you to think about who we are as a species and why we are so bad at all types of relationships.