I get that people don't like this movie. I myself rented it this previous Halloween weekend, hoping for a good monster movie, despite the costly price tag on my pay-per-view service.
Still, this movie surprised me. I thought it did a better job than most Hollywood fodder at making us care about the protagonists, and while I still expected and hoped for some good monster action once our emotions were stirred, I still wasn't disappointed. It was simply that the message of the film was not one of monster horror per se, and although that was what I was looking for that unfulfilled desire didn't blind me to the value of the film. I think a better question would be, who are the monsters in the film? There are more than just the extraterrestrials.
Within the reviews I have seen comparisons to many films. Prior to reading them I myself found comparisons to District 9 and Cloverfield. The thought of a government cover-up crossed my mind when I mistook the Wall for a research structure located deep within the infected zone while watching the trailer, although I didn't immediately make the comparison to The Mist. I also didn't see a comparison to Apocalypse Now that another reviewer alludes to, but it would be interesting to hear more of what that reviewer saw that I didn't - or I'll just have to watch the two one after the other sometime in the future and come to my own conclusions.
Needless to say, there are many precedents to this film. There is one that stood out to me that I did not see anyone mention, and that is Andrei Tarkovsky's Stalker. Both Stalker and Monsters have a Zone that was created by an extraterrestrial event, both have guides through the zone ("coyotes" in Monsters and "stalkers" in Stalker), both are littered with civilian ruins alongside military machinery that has been conquered by the extraterrestrial presence and overgrown by nature - the most striking visual similarity, and both lead their protagonists to introspective insights as a result of their journey through their respective zones.
Now, I tend to give a filmmaker the benefit of the doubt, especially with independent films, that they are at least attempting to be poetic. (Let Tarkovsky roll in his grave, but if the scene of the building being knocked down to reveal a church in the background from The Steamroller and the Violin wasn't symbolic, especially against the background of communist USSR...) So I asked myself the question, what does the film title allude to? Without going into detail to give too much away, I think a theme subtler than others in the film has to do with what happens when nature - including human nature - is left unfettered by the physical and social constraints placed upon it. One of the guides who lives in the zone in Monsters observes that the creatures act like wild animals, they leave people alone if people leave them alone - but they get pretty angry when the US planes come in and bomb them. There's plenty of idealism to be mined there.
I really liked this film. It's not going to be one of the classics in my collection necessarily, so it probably deserves a four personally, but I'm giving it a five here because I think it rises above the dumbing down the majority of American films have seemed to suffer from lately. Or perhaps I'm being too critical - not all films can be more than just entertainment to stave off the boredom of modern life.
So ignore my own existential BS and see the movie. You might find it worthwhile.