I think we've been ruined by Prestige Television and you're honestly just expecting too much from it.
Where both episodes failed for me simply was lack of any tension and feelings of horror. The original films were defined by a feeling of the aliens being completely inescapable and being stuck in tight confined spaces without much hope of escape. The first one everyone stuck on the Nostromo, the second being stuck in an abandoned planetary settlement, third inside an inescapable prison... The rest, well, that's where we begin to lose that sense to begin with.
I mean, I kind of expected it to fail on horror fronts due to it being on earth. Lots of places to escape to.
I still found it pretty fun, despite failing that, but maybe I just went in with lower expectations.