Trust no one.
Why it is hard sci-fi
A long-running procedural with two parallel arcs. The case-of-the-week structure runs as quasi-scientific investigation with a working pair of agents, one as the believer and one as the sceptic. The conspiracy arc engages with a hidden federal program that has been negotiating with extraterrestrials since the 1947 Roswell incident. The shows hard episodes hold to one mechanism and follow it through.
Science inside it
Forensic procedure applied to anomalous events, biology of hybrid organisms, the shape of a black-budget federal program, and a long-running engagement with the question of how to authenticate a single piece of physical evidence under continuous denial. The shows weakest episodes drop the rule. The strongest hold to it.