This is a movie about an underground laboratory where a couple of scientists are researching an ancient artifact for a private corporation. A group of mercenaries are sent down to try to get the situation back in control but it's far too much for them to handle and they come across a couple of escaped human test subjects instead.
Okay, first of all: The movie title is entirely misleading. It may have zombies and aliens in it but the zombies are nothing more than possessed humans and the alien(s) only show up in a few very badly made action scenes. This is not even close to Alien VS Predator! Just to get this clear.
The mercenary team consists of cliché archetypes which all have pretty generic personalities. You have the leader who "doesn't leave anyone behind", the badass that "is in for the sake of fun and " the loner that "needs help from no one". The rest of the team gets killed off pretty much in the first scenes they're in, screaming while shooting down a corridor against the "zombies". The mercenaries are devoid of any real personalities except their cliché archetypes which they don't pull off that well either. It seems all of them wants to be the main protagonist at the same time and it even switches between them a couple of times. The dialog is very straightforward and doesn't give the impression that the speaker is the one actually coming up with those lines. The movie itself is fairly intelligently made but quite slow pretty much all the time. The action scenes gives no enjoyment because they're horribly filmed with far too many close ups and shaky cameras.
So from what I can gather the story is about a couple of mercenaries that decend into this underground laboratory. To get to a couple of human test subjects... only to give up and try to escape again. They do this by trying to climb through the ventilation system but it's far too dangerous in there so they give up that plan and barricades themselves inside a room together with the person responsible for the events of the facility, the antagonist. Most of the film unfolds in this barricaded room where they discuss and send a few men out to try and scout out some options.
Anyway - this movie is perhaps not the worst movie ever made but it certainly deserves a 1 for the misleading title alone and since I cannot go any lower that's what it'll get. If you know what you're in for perhaps you could enjoy the movie far more than me but it was a waste of money as far as I'm concerned.