Were-Monster" style comedy, part 24 episode, and part spinoff setup. The results were a bit mixed, but far better than this season's previous Chris Carter episode, "My Struggle."
Taking those elements in order, the comedic elements of the episode felt like the most successful to me. Most of it came from the juxtaposition of Mulder and Scully against the newbies, Miller and Einstein. (More on them in a bit.) But the most concentrated dose of zaniness came in Mulder's "magic mushroom" trip, a truly hilarious sequence that had it all: dozens of amazing reaction shots from David Duchovny, cameos from X-Files characters past, nods to Mulder's fetishes, and a crazy dance number set to the perfectly schlocky "Achy Breaky Heart." Fantastic and funny, it was the clear highlight of the episode.
The actual case itself was usual in that it was not an "X file"; only Mulder's approach to it (and, to a lesser extent, Scully's) made it one. I do like the angle of putting the duo on a more conventional FBI case, but I'm not sure that it was a good idea for that case to be about Muslim terrorist bombers. The episode was already trying to say a lot about the nature of God and faith, about communication and love, and I'm not sure that stirring such a hot button issue into the stew helped them. It's not that a TV series can't take on Islamic terrorism, nor even (I suppose) that a series deciding to dramatize that has any obligation to express nuance on the subject. (24 seldom did.) But it felt like this series, this story, did want to say more than it really had time to express. I'm not sure the bookend scenes about the trumpets from on high was enough.
So then, what was going on with Miller and Einstein? Was this a one-off joke pairing Mulder and Scully with young dopplegangers, or an actual and earnest attempt to position characters that might replace David Duchovny and Gillian Anderson if they should decide not to return for more episodes? I'd say it was far more successful as the former than as the latter. It's nothing against either Lauren Ambrose or Robbie Amell, who played the young agents -- it's just that there really wasn't anything to them beyond aping the regular characters. The jokes of their similar appearances and similar (if exaggerated) behaviors worked. The idea of actually watching more episodes with two characters exactly the same as the original characters, but not actually them? No... there's no way they could be doing that.
Enjoyable overall, I'd give "Babylon" a B. That leaves just one more episode before this short experiment in "maybe you can go home again" comes to an end.