Fox never quite grasped what was the big draw with Predator. It was an ARNOLD SCHWARZENEGGER film! Arnie fighting an Alien. That's what it was about. The same goes for the Aliens series. It was about Ripley (Sigourney Weaver) vs. the Aliens. It's been diminishing returns ever since these films deviated from their hedgehog concept, with every subsequent film aping the original recipe while getting more-or-less diminishing returns.
Here is my bet. If the next Predator film brought back Arnold Schwarzenegger in a starring role it would be a hit. If the next Aliens film brought back Sigourney Weaver and the surviving stars from Aliens and continued where that movie left off, it would be a hit. Other wise, every film skirts around the recipe yet does not quite deliver.