And you can do fine with that formula as long as the humans are interesting and you actually end up caring for a few. That's been the issue plauging the AVP films, every human in them has been expendable, you almost root for them to die, there's no one you care to see get out. If you can't care about the human characters the movie's going to suck because most of the time, 70% or more of the film is spent with them.