Ah, the Borg. The Catch-22 of 1990s-era Star Trek. They were a brilliant invention as a one-off major threat to our protagonists: implacable, technologically superior, and not interested in negotiating to resolve differences. But what do you do with them after exploiting their technical vulnerabilities to defeat them in "The Best of Both Worlds, Part II"? "I, Borg," well over a year later, answered that by going in a completely new direction — using the Borg not as a visceral threat but as a device for moralizing. (I thought that was a brave narrative choice, and one that demonstrated that the Borg would have to continue to evolve as storytelling devices to avoid becoming a rehash.)
Now we have "Descent, Part I," which attempts to put the Borg back in business as a visceral threat, but in the process changes everything that the Borg once were (and, of course, what made them originally interesting). Instead of a hive mind bent only on assimilation, now the Borg are brutal warriors who have individual identities and names, who attack a Starfleet installation and kill everyone there. The Enterprise arrives to answer the distress call and engages the Borg in a firefight; one Borg vows revenge when his fellow soldier is killed.
This change in behavior is admittedly the point; a big part of "Descent's" story is the crew trying to figure out how and why the Borg have changed so dramatically. Could the reintroduction of the individualized Hugh into the collective have somehow caused this radical shift? (The story is cagey on the point of whether this might be isolated to only a small subset of the Borg, who have a badass-looking new ship design.)
As season cliffhangers go, "Descent" is middling; it's better than "Time's Arrow" but it's certainly no epic like "The Best of Both Worlds" (or even as involving as "Redemption"). By this point, season-ending cliffhangers had become so routine and obligatory that it would've been a radical act if this hadn't been a setup. I guess that's part of the problem here; "Descent" is mostly setup, and doesn't even try to exist as a story that can be truly satisfying on its own. Oh, sure, it's entertaining enough. But do we believe for one second that any of its questions will be answered until season seven?
I guess for now, let's take a look at some of the admittedly interesting story points. Data experiences anger during the initial encounter with the Borg during hand-to-hand combat. He later attempts to recreate the emotional outburst with simulations of the attack. Could Data finally be evolving to experience emotion? (This is one of the story points that is actually addressed before the "to be continued" sign, but in a manner that turns the character point into a plot point.)
I did find interest in the scene where Admiral Nechayev chews out Picard for releasing Hugh in "I, Borg," because it presents the legitimate and pragmatic alternative viewpoint arguing for survival: that the Borg are a threat that must be destroyed, and we couldn't afford to let personal moral conviction get in the way of that. Picard even expresses some hand-wringing over it. It was never a cut-and-dried situation in "I, Borg," but it's nice to see some actual fallout from that decision.
So the Enterprise pursues the Borg ship, which sends an attack boarding party, which results in the capture of a Borg named Crosis (Brian J. Cousins), who talks of a mysterious One who helped bring a focused individuality to these Borg. Crosis might best be remembered for his shtick of reciting the fastest ways of killing various humanoids ("Death is immediate"). His conversations with Data reveal that (1) Data's emotions are actually being sent to him via some sort of signal in an attempt to take control of him (thus robbing the story of character value and turning Data's emotions into a plot point) and (2) a Security Guy in the brig can be standing right there while Crosis seduces Data in a rather alarming exchange of dialogue, but apparently Security Guy won't do anything with such information. Ultimately, Data flees in a shuttle, leading the Enterprise in pursuit.
It's about here where the episode drops all pretentions of trying to continue telling a story and falls prey to Two-Parter Padding Syndrome™. The attempt to track down Data is purely procedural and does little to actually advance the story. Ultimately, Data is tracked to a planet, where much of the senior crew beams down to engage in a search. They set up a command post and look at maps and discuss search strategies and stuff, and you realize that none of this is actually necessary except to pad out the running time before we get the final twist and inevitable "to be continued" card.
The final twist is perhaps one twist too many, and comes out of left field. It turns out that the One pulling all the Borg's strings is ... Lore. And now Data has joined his evil twin in their announced plan of together destroying the Federation — bwahahaha! This is all hook and no motivation, all setup and no payoff, and it cannot fairly be judged within the confines of just the first half. So tune in next season, as they say. As finales goes, "Descent" is mostly fine and reasonably paced, and introduces a number of intriguing elements — but it ends on kind of a head-scratcher. As for its grade, we'll go with Incomplete.