AvP is a movie that has not only abandoned the concepts of character and plot, but actively rebels against them. In this way it is something of an experimental film. One can imagine some snooty French filmmaker sitting in a chateau in the countryside pondering the existential question "What if we made a movie that was nothing BUT Deus Ex Machina? A film where all plot advancements and untanglements were literally caused by some God Machine? Where nothing anyone did really mattered, and where the only choices the characters could make would be what attitude to have when death came for them?"
This is not inherently a bad idea, but if the snooty French guy made it he would surely add an element of humor or at least philosophy to soften the nihilistic brew. He would also have the decency to admit he was making a statement or punishing the audience instead of trying to entertain.
Paul W.S. Anderson does none of those things. Instead he chooses to ignore the characters, ignore the audience, and focus on making CG monsters slash and shoot at one another. The Deus Ex Machina he regularly employs (the movie takes place inside a pyramid that reconfigures itself every 10 minutes, helpfully opening passages towards or away from whatever the characters need to encounter next right on cue. This entire Deus Ex Machina set up is itself Deus Ex Machina because it's claimed that it's based on the fact that the society/creatures who built the thing operated on a numerical system based on 10. There is no explanation as to why they would use the same second we do as a unit of measurement, one that is completely arbitrary, nor of course why such a society would use a sixty second minute.) doesn't teach us anything about humanity or fate or nihilism. All it does is pamper his infantile "big monster go boom" desires.
Sometimes he wants the monsters to smash up the stone pyramid in such a way that one wonders why there is no evidence of the dozens of implied battles that have taken place there before this one. Sometimes he wants them to stand off against one another like boxers in the middle of a ring, even though this would seem to be reasonable behavior for neither. Occasionally he wants them to breakdance, and they do.
Now one might argue that Paul Anderson is merely meeting the needs of the marketplace with AvP. People wanted to see the two species do battle and breakdance and whatnot and that's what he gave them. If that's the case, though, why is the Deus Ex Machina necessary? It doesn't speed things up, the first battle between the two takes place around the 55 minute mark of a 90 minute film. It doesn't add to tension, in fact the characters become utterly disposable and interchangeable because nothing they do matters. They can spend 10 minutes following the most rational plan anyone could think of, only to have a trapdoor swing open beneath them and disgorge a swarm of deadly Aliens. On the other hand they could follow the most idiotic path imaginable and emerge unscathed because a door shuts behind them suddenly or a weapons cache is seemingly randomly exposed.
In the Alien franchise there is already an example of how to make this kind of picture without resorting to complete garbage. It's called Aliens, it was made by James Cameron, and it features both exciting frenetic battles and a strong plot/character combination. In that movie the actions of the characters carry consequences, and while sometimes things happen beyond their control it is not for arbitrary reasons. There is no reason that AvP could not have been the same sort of film, if you don't count Paul W.S. Anderson's complete lack of talent.
The only question left is why it was left up to him to make this movie. Why Hollywood would choose to hand $60 million and two of its most popular franchises over to a confirmed hack. There's only one reasonable explanation, of course, short of his performing sexual favors for a studio head.
Deus Ex Machina.