Both the Alien and Predator franchises were run into the ground with their sequels, the Predator meeting an earlier fate. It's been ten years since we last had a run in with the Aliens and 17 since the Predator tried to tear apart Danny Glover. Both come back together in the long time coming Aliens vs. Predator, a meeting between two of Hollywood's most vicious.
Killing Alien vs. Predator from the start is its complete lack of acknowledgment of the films that came before it. Director and writer Paul W.S. Anderson claims to be a huge fan of both franchises, so why would he ignore them? The timeline is completely messed up, the Predator befriends a human (in what has to be the film's most ridiculous idea), and it doesn't even follow its own history. The Alien incubation period is absurdly fast compared to previous movies. It's a mess.
That's still not the biggest complaint. The worst change you could do to this film is take away what made the originals such a treat for horror and sci-fi fans: the gore. No, it's not the director's fault, but the studio's. Aiming for the PG-13 rating takes all the fun out of the deaths, not to mention the horrible cuts to get away from any scene that would be even mildly brutal. Even the director’s cut, included on Blu-ray, is still not up to par.
There is minimal time spent on developing characters, not that it really matters anyway. The action takes about a half-hour to build, giving plenty of time to develop, yet it never happens. Going with another unknown female lead was a nice touch. Unfortunately, she is the only character you'll ever really know anything about. If you haven't actually seen a previous movie in the Alien series, good luck trying to figure exactly what it is the Weyland Corporation does.
The eventual "meeting of the minds" is the only thing that goes right, and it occurs almost exactly at the hour mark. There are two major battles stuck in between countless smaller ones. Those two are spectacular on a visual level and a real treat for those special effects fans. The combination of great puppetry, men in suits, and CGI is handled surprisingly well. Anderson went almost entirely for standard effects, using CG only when necessary. He deserves major credit for that, though it hardly makes up for the rest of the film.
Eventually, you realize the movie is nothing more than a 90-minute trailer. Every shot of the monsters squaring off seems primed to show up somewhere during the ad campaign (how many times do we need a close up of the Alien's lip curl?). This is just too far from the other films.