As I explained in other threads, the dominant genre or probably theme employed by the first movie is horror. That's because the creature is fully revealed only in the last few scenes of the film.
Obviously, they could no longer do that for the second movie, which is why action was employed.
Another genre resembling detective fiction was used for the third, i.e., how to kill the creature.
The fourth follows something similar in conspiracy films, involving scientists, the military, mercenaries, etc. Although the third looked like the proper end for the franchise, i.e., if Ripley is considered the center of the story, it is still open-ended because it is implied that the company or at least other groups would try to profit from the creatures. Which is what happened in the fourth.
But the fourth still has no closure given the point that Ripley's character is brought back and the aliens still pose a thread to humans. Given that, the only genre I can imagine that is different from those used in previous films and that will finally give closure is major conflict and whatever tech needed to destroy the xenomorphs, or at least give human beings a fighting chance to do so but at incredible costs, thus allowing for a return to the bleakness of the first film.
With that, it's obvious that the prequels would employ other genres, and in this case looks like something involving scientific discoveries concerning the origins of the creature and various plot twists connected to that. The idea is sound, but there were problems with the story, notably the introduction of a star map discovered and connecting it to "Engineers." Perhaps a more elaborate tale should have been constructed, and that would certainly make at least the first film look like 2001 rather than an Alien film. If similar principles were applied to the next movie, then it would have been different from the recent mess, where the same theme involving origins was mixed with elements from Alien and Aliens.