I understand the rationale behind the choice to have a younger crew, scenario-wise, but there can also be commercial motivations behind it and I must admit I think that there are already too many (horror) movies with insufferable young characters (to please the YA audience), thus I have some apprehension about this aspect.
I agree with solace97. The reactions to the alien in the first movie were great and conveyed the true alienness of the creature, the horror and awe of the characters when they saw it in its adult stage. However, with the second movie, the multiplication of the creatures diminished this aspect and although there was terror, it was less linked to the appearance of just one xeno. There are passages of the third movie where the xeno is impressive for the audience in that sense too. In Covenant, I found the tiny bit where the Protoxeno enters into the hangar at the end to convey that same impression. The problem is also linked to the degree of exposition to the creature, its screentime, and other things.
