It's the conclusion of a Mythology Episode trilogy and I'd disliked the other two episodes. It's also an X-Files season finale, so one's expecting seat-of-the-pants nonsense that prioritises impact over storytelling. Was my doom and gloom justified? Ultimately... it's pretty laughable. It can be exciting, mind you. It's a good example of Chris Carter's momentum-led plotting. It's killing or pretending to kill important characters. There's a good scene at the end.
However, it's also a William episode. He's still a knob. Why's everyone looking for him? He's the show's latest McGuffin, but are psychic powers such a big deal in the X-Files universe? The episode also pumps him up with too many abilities, so no one can threaten him and he can do anything he likes. Why should we care? Possible answers:
(a) he's Scully's son. That's a convincing reason for Mulder and Scully to care about him, admittedly.
(b) overblown dialogue. "The person who controls your son is the person who controls the future." "Your son has what everyone wants. What people would kill to have." "We need to find him before they do. Everything depends on it. Every last thing in the world."
William's not just scum, though. He's also stupid. He does something gratuitously horrible to a trucker who's giving him a lift in his truck. It would have been a miracle if he hadn't crashed. William could expect to survive that, but what about the trucker? (That was more reprehensible for me than making people explode, because the truck driver had done nothing wrong.) Result of being a bastard: William has to walk along a highway in the rain.
Later, he becomes self-pitying.
Oh, and he "just kind of became a criminal" as a teenage phase. He'd make vehicles collide for laughs, etc.
This eviscerates the episode. It's exciting and well made, but its McGuffin is a waste of oxygen. Several characters die or possibly die, incidentally. Some deserved better endings. Others obviously aren't dead... well, unless the show never returns, in which case maybe they are.
Surprisingly, the episode doesn't end on a half-arsed cliffhanger. Instead, it does something fan-pleasing and biologically implausible, justified by Mulder saying "that's impossible". Um.
Mythology episode questions:
DENIABILITY (William): as before.
DENIABILITY (the deaths): ahaha, lots.
FOLLOWED UP: I don't expect they'll ever make any more.
Is this episode good? No. Is it a strong end for the franchise as a whole? Absolutely not. (Being a two-parter might have given it more weight, incidentally. At 43 minutes, it's a bit of a throwaway. Doubling that might have forced Carter to write a proper story.) Is it a worthwhile season finale, though? Sort of, maybe, in a bloodbath way. Look at all these important people getting shot! It's moderately watchable, at least, and I'm probably an outlier in how much I think William damages the episode.
"If this is my life, I don't want to live." (Well, I'm not keen on you staying alive either.)