I had high hopes for this episode for lots of reasons, and for the most part it met them. One of my favorite parts of every Darin Morgan episode is how he likes to cut Mulder down to size. This pose/line from "Humbug" sums it up perfectly:
So I wasn't surprised to find Mulder doubting his abilities and his beliefs right at the beginning of the episode. The only thing is, I feel like this blow was softened a bit because he already went through the same crisis in the first episode (although there it had a dramatic bend). Still, though, I prefer the panicked Mulder to the confident Mulder almost any day of the week. Morgan episodes also have those memorable characters that drop into the M/S's lives in a significant way (like Clyde Bruckman) or those small-time characters who are just there to color the world (like The Enigma and Bambi). This episode had all sorts, including Rhys' character (who I thought was great) as the former and the glue-sniffing hillbillies, the motel manager, and Shangela ("Halleloo!") filling out the latter. I wasn't wild about Kumail's character, who was pretty shallow and one-note; I think his humor may just not gel with the series. I wish they held off on revealing the "twist" for a bit longer, but it was incredibly clever. My favorite bit may have been when Rhys tried to get Mulder to murder him ("No, not the gun!"). This is the toughest type of X-Files episode to nail, and they may have hit about 85% of the target, but I still loved it.
There was some good meta-stuff in here, too, like the deconstruction of the "Scully in peril" problem that many people had with lots of early episodes. The whole "Scully is immortal" thing was also a huge, huge bone of contention among fans since Season 3 (i.e., whether it was canon or not), so that was a good gag, too.
Also, RIP Kim Manners!