Parts one, two, three and four of looking at Star Trek: Enterprise's third season Xindi Arc.
"Home", the third episode* of the fourth season of Star Trek: Enterprise served as an epilogue to the Xindi Arc, primarily by dealing with the emotional fallout of the character subplots. Specifically, it focused on Capt. Archer, and Trip & T'Pol. Both of these aspects work fine in terms of the episode itself. For Archer, he's somewhat broken by the things he did in the Delphic Expanse. He specifically mentions the theft of the warp core, which as mentioned last week, was his greatest sin. But beyond that, his optimism about exploration in general is broken, despite the fact that things did end relatively well. This ties into the one other minor plot thread in "Home"-- the Enterprise crew might be hailed as heroes, but there are some people who aren't thrilled with the fact that they had spent two years running around space saying, "Hey, we're from Earth. Come on over and smack us around, why don't you?"** For Trip & T'Pol, their subplots of his grief over his dead sister (more or less resolved in "The Forgotten") and her emotional damage due to self-inflicted Trellium exposure*** dovetailed into their semi-romantic friendship. So they go to Vulcan together, and deal with T'Pol's family drama.
So, in the end, what worked, and what didn't in the Xindi Arc?
For me, the broad brushstrokes worked: a threat is presented, and to defend themselves from that threat, core principles are challenged and strained. Despite that, in the end, it is those core principles that saves the day: friendship is achieved with (most of) the Xindi council, creating a lasting peace through conversation.
What didn't work, though, is how things went in terms of character. Specifically, character never tied into plot in a real organic way. The closest was with Archer, who's moral center was challenged, but that balance between what he needed to do and what he had to bring himself to do always came more with an axe instead of a scalpel. Archer doesn't get a slow descent into darkness. He gets one questionable moment (putting a pirate in an airlock to get answers) and one really bad no-win scenario (the theft of the warp core). Beyond that, what does he do? True, he doesn't blow up the refinery in "The Shipment", but that seems less of a Moral Choice, and more thinking in terms of long-term strategy: going in guns blazing isn't the smartest thing to do if you've only got one shot at that, and you haven't found the right target. In the final third of the season, Archer seems ready-- even eager-- to die for the cause, but why he's gone semi-suicidal isn't really explored. Despite Daniels coming from the future TWICE to tell him, "Yeah, you're important, you can't die," he seems hellbent on it anyway. There is a bit of lip service of not wanting to order someone else to their deaths, but that wasn't something ever really discussed.
What also didn't work was the lack of focus. Most of the first two-thirds is spent wandering: some of it ties to the Xindi or the Spheres, but the rest is largely irrelevant. It doesn't move the plot, nor is it called back later. So it doesn't serve a purpose. Perhaps if it had done more worldbuilding of the Expanse, creating encounters that mattered, so that they could be called upon at the endgame, then it would have seemed more meaningful. And that would have also tied into a Trek solution: humans build communities, create allies, so when the chips are down, friends come to their aid. But no species in the Expanse really were important other than the Xindi and the Spherebuilders. The Spherebuilders were, at the core, the Big Bad, and the Xindi-- while having solid individual character-actors-- themselves had no definition beyond "five subspecies in fractious alliance".
As counterpoint, I might present the end of Farscape's second-season. After two seasons of more or less random encounters-- those stand-alone episodes-- the crew is faced with having to do a Big Crazy Plan. And to pull it off, John Crichton calls on various species and people they've met along the way. Now those stand-alone's tie into the solution, and to worldbuilding as a whole.
But, credit where it's due: they took chances, and in the end, created something that had value. In my recent re-watch of it all, I was largely entertained. With a little more streamlining and focus (which, admittedly, in the world of episodic television, especially a decade ago, is challenging), it really could have stood out as something special.
*- The first two episodes had nothing to do with the Xindi storyline. Instead it involved time-traveling Nazi aliens, and served mostly to tie off the Temporal Cold War storyline, which had never been very well handled. "Zero Hour" ended with an exceptionally bizarre Hail Mary of a cliffhanger, and those episodes are at best a serviceable affair of digging themselves out of that hole, as well as the entire TCW one.
**- Though you have to wonder why, when the Xindi weapon showed up, Earth's only defense was, apparently, a single Andorian cruiser. It made for some satisfying drama, but didn't make much sense.
***- A clumsy drug-addiction metaphor.