Failure to write good human characters is one of the bigger flaws with the avp movies. Wolf being lackluster, aliens being weak aside, the human characters should be the backbone of the story. It's their experiences we're living the story through. It's not just about aliens vs predators, it's about us trying to survive the war of the species.
They can add colonial marines, they can add stronger aliens, they can even set it in space, but all the sound and spectacle and fury doesn't matter if the human characters exhibit all the personality of cardboard. I'll take Machiko over Ricky the indifferent pizza boy anyday.
Until they address this issue, I'd rather the series be left in stasis.