So, the episode sucked, but it was a pretty entertaining event? I'm not following, sorry.
What was so bad with the ending?
The "craptastic" comment referred to this particular episode; the "overall pretty entertaining" comment referred to the whole 6-episode event. This whole deal has been billed not as "The X-Files Season Ten," but rather as "The X-Files 6-Episode Event." They even had their own logo referring to it as that.
As for what I didn't like about this episode:
- Cancer Man's survival strains credulity
- I never felt Agent Reyes was a suitable replacement for Agent Scully in the original series, but even she deserved better than to have "sold out" and become Cancer Man's willing lackey
- There wasn't much "mystery" to be solved in this episode; it was all very straightforward "evil Cancer Man's killing the human population off except for those he's personally selected to survive" [insert evil laughter here]
- The cliffhanger ending completely sucked, especially if this is a one-time deal and we don't get a new series picking up where this episode left off come this fall to provide some explanations
- The situation presented in the episode either comes off as "the human population is killed off" or "Scully single-handedly saves the world with her magic alien DNA" - neither of which fits in with the normal X-Files "feel" of old
- Scully's not going to be able to plausibly produce enough antidote from her alien cells to save much more than her own hospital staff, let alone the entire human population of Earth, so anything other than a "humans die off" endgame is going to come off as pretty cheesy
- Scully rushes the antidote to Mulder (driving through impassible traffic jams on a bridge to do so) to save his life, but then announces that the only thing that will actually save his life are stem cells from their missing son, William - say what? (If that's true, then Mulder's the only one who can be saved among those who don't have Cancer Man's specially-selected alien DNA? Sucks to be the rest of us.)
- The UFO showing up at the end is completely unexplained
This just didn't feel like an episode of The X-Files to me, and it ended the otherwise enjoyable 6-episode event on a sour note, especially since I haven't heard if there will be anything further coming after this. Your mileage may well vary - but I'm sticking to my feelings of "craptasticness" for this episode.
Johnathan