America Saves the Day: Puny Brits need American badasses to show them how to be men again. Subverted in that they cause the destruction of the castle, many needless deaths with nothing to show for it, Van Zan dies rather spectacularly, and Quinn is the one that actually kills the male dragon.
An Axe to Grind: Van Zan's hideous looking axe that he uses to finish off the dragons they shoot down.
Antihero: Van Zan. Depending on how you look at it Quinn might count as an antihero for much of the film.
Apocalypse How: Class 2 (fall of civilization) with the possibility of it growing into a Class 3 apocalypse (human extinction) if the dragons outlast the humans. The survivors begin to rebuild after the dragons are defeated, bringing it closer to a Class 1 event. Shades of Class 4, due to the humans' and dragons' mutual success in devastating the biosphere.
Apocalyptic Log: As the introducing voice over explains what happened after the first dragon awakens, we see a newspaper montage covering different stages of the dragon apocalypse, from the first scientific articles to the war itself. A nib pen, presumably Quinn's, scratches out a message to his adopted son.
Awesome, but Impractical: The entire "skydiving with a metal net to make a dragon fall to its death" tactic the Americans use. Talk about going around the world to get across the street.
The Chieftain tank — its BFG is good for intimidating settlements, not so for blowing up flying creatures.
Badass Boast: "There's nothing magical about them; they're flesh and blood. You remove the heart, you bring down the beast!" Also, after being told that the sky is the dragon's territory; "No, that's my territory. That's your territory. They're just renting it."
The Chains of Commanding: Being The Hero sucks. Just ask Quinn about it. He's responsible for an entire community, has to make hugely unpopular decisions for the good of everyone, and honestly has no real clue what he's doing. The reason he's in charge? Because someone has to be and everyone agrees he is. No wonder he's training Jared to take over.
Doing in the Wizard : How the dragons make fire, via a reaction of two chemicals similar to a bombardier beetle.
Dragon Hoard: When the young Quinn first stumbles into where the dragon is hibernating the walls are covered by Pyrite...or possibly gold. We didn't get long to look at it before all the burning and the death starts.
The Dragonslayer: Van Zan (and his fellow Americans) are all specialists in slaying dragons. They have knowledge of the dragons' weaknesses and exploit these with a range of specialized equipment, including a tank and a helicopter which can drop troops onto flying dragons to force them to land.
Easy Logistics: Despite the complete collapse of human society, an entire armoured division is able to still support itself. You have to wonder how much fuel they expended just to get to Britain in a world where presumably there is no more oil extraction.
Though by Van Zan's own admission, they're essentially running on fumes by the time they show up at Quinn's castle.
Elemental Baggage: Averted. The film explains how the dragons create the fire: two glands produce "natural napalm," which ignites upon contact with the air.
Eye Scream: A mild case - Quinn gets a faceful of the dragon's fire fuel when he first discovers them, which makes his eyes turn blood red.
Expanded Universe: The video game of the movie shows juvenile dragons, who are ground-dwelling creatures looking rather like dinosaurs.
Fake-Out Opening: The film starts with twelve-year-old Quinn meeting up with his mother on the construction site where she works. We learn fhat Quinn's lost a £3000-a-year scholarship and that his (presumably wealthy) father is no longer in the picture, and for a minute it looks as though the film's going to be a serious picture about Quinn and his mother struggling to make ends meet... Aaaand then the dragons appear.
Feed It a Bomb: How the male dragon is killed: shooting explosive-wrapped crossbow bolt into its wide open mouth.
Final Boss: The male dragon, whose defeat spells the end of the entire species.
Good Is Not Nice: Van Zan. Quinn can look this way to certain members of his community. As Creedy puts it "I'm your best friend. And some days, even I don't like you."
He Who Fights Monsters: Van Zan is heading there at a rapid pace. To quote Alex after his fight with Quinn: "He would have killed you. He doesn't feel things. It's the only way he can do what he does."
The Hero: Quinn to the castle community and the film.
Hero Killer: The big male, who is the original dragon and responsible for the death of Quinn's mother. When Van Zan tells Quinn about him, Quinn is visibly scared, and even Van Zan (the man who will take on a dragon with a chopper and a harpoon gun) wants a small army with him when he goes hunting for it. It even has the reputation you'd expect: Quinn relates an incident wherein a group from Pembery went to London and disturbed him, resulting in 90 deaths and the destruction of the castle. The male subsequently goes on to wipe out Van Zan's army, burn the castle down, killing AJ and Creedy in the process, cannibalise several of his own and kill Van Zan. On top of all that, his vast size makes him the only dragon that's easily distinguishable and recognisable.
Meaningful Echo: Early on Van Zan demands to speak to the person in charge. Everyone turns to Quinn. "Well, that'd be you then." The line isn't said again, but a constant theme of the movie is the community's dependence on Quinn as the leader. At the end, Jared rides up to inform Quinn that they have a message from France, and that "They want to speak to the person in charge." Quinn by this point can safely look at his protege and say, "Well, that'd be you then."
No OSHA Compliance: In the opening scene none of the workers display any objection to a child (Quinn) entering a construction site without any protective gear. When their digging hits an unexpected cave, one of the workers even suggests Quinn go take a look inside. To top the stupidity off, once Quinn comes rushing out of there, the same worker keeps saying "It's not safe!" If it's not safe, why the hell did you have a child go in there?
Not So Stoic: Van Zan is in visible pain when his comrades are killed.
Our Dragons Are Different: Oh, so different. They have only four limbs, connected by a bat-like membrane of skin like a Wyvern.; they breathe fire through a chemical reaction; and there is only one male who fertilizes all the eggs of the females like a male salmon.
The first point was likely a Shout-Out to Dragonslayer and its villain, Vermithrax Pejorative. Also for a more realistic look for the dragons (considering that there are no and have never been vertebrates with more than four limbs), along with the napalm-like fire.
Parental Abandonment: Quinn, Jared, and likely most of the kids in the community have lost their parents.
Pyrrhic Victory: The first time we see Van Zan's dragonslayers in action, things go horribly wrong and he loses three men to bring down one dragon. It's implied that while their strategy doesn't always go to plan, this particular outing was an especially poor showing.
Reality Ensues: Yeah, Van Zan is a badass and all that, but come on people, no-one is going to survive leaping through the air from the top of a high tower, at an 80ft dragon, with nothing but an axe, when it's heading right for you.
Red Shirt: The skydivers know they've got a limited life expectancy.
Shout-Out: The re-enactment of the Star Wars scene. In the post-apocalyptic future, Star Wars has apparently become legend (and one of the few entertaining memories/stories available to members of the camp).
Tank Goodness: The tank Van Zan's crew has with them causes noticeable concern among Quinn and his community.
Testosterone Poisoning: Matthew McConaughey plays his character this way. Trivia has it, that McConaughey WRESTLED COWS to get his build for the movie.
Trivia also has it that, after several failed attempts at a scripted fight between Van Zan and Quinn, the two actors decided to simply beat the snot out of each other for real.
Too Dumb to Live: Eddie, a member of Quinn's community. First he tries to pick the crop out of season (admittedly it's because he has starving kids, but still...) attracting a dragon in the process and costing them half their crop. Later on, he joins up with Van Zan's doomed raid on London.
His children seem to have inherited that same lack of IQ, as one when rescued by Quinn in the fireproof trucks, decides to stand in the exposed turret without a protective suit and thus gets barbecued.
Van Zan's whole paratrooper approach to fighting dragons (because falling helplessly through the air, vulnerable to attack from any side is the best way to fight giant, flying, fire-breathing monsters)
What the Hell, Hero?: Van Zan tears the brits a new one when they throw a party; to them, they're celebrating the death of the dragon that had devastated their food supply. To him, they're celebrating the death of one dragon and three of his men.