I'd like to clarify a couple of things. I disliked the Caeliar because I didn't like the way they just swept up the Borg
I did. I think that the thing about the Borg is that once you start playing with them, you either need to have them go all-out against the Federation and win, or be utterly and permanently defeated. They're just too powerful otherwise for the third story option -- "The Federation defeats them... THIS TIME! But they're still out there... Somewhere!" -- to remain credible after it's been used so often. It undermines verisimilitude utterly if we take that option again and again. You need to either shit or get off the can.
and acted all superior in a cold logical sort of way.
Well, that was the point of their arc -- that they went from this aloof, cold, arrogant power to realizing that they need to be more humble, more heterogeneous, less aloof, as a result of their contact with Earth and the Federation. They adopted Federation values, and in doing so, saved the Federation and themselves.
I didn't like how they insisted on captivity and how that impacted on the story with long chapters about how the crew of the Colombia were adapting to aforementioned captivity. It's not exactly a new thing in Trek to have some alien species keep our heroes captive and fail to understand as the captives struggle to contend with the luxurious conditions the captors have provided.
But those scenes weren't about, "Oh, it's a luxurious cage but still a cage." That sub-plot was about how the nature of identity relates to our external circumstances, about how, so often, we become our own prisons. It's a much more sophisticated sub-plot than your standard "Starfleet captain gets captured by aliens who want him/her to like his/her cage."
I wasn't too keen on the Borg explanation. I disliked the way Humans are involved with the origin of the collective and felt it was unneccessary to have any connection between the Borg and Earth, whatsoever.
The sheer force of coincidence that a group of cybernetic organisms would happen to call themselves by a name that's identical to the suffix in the English word "cyborg" isn't enough to demand some sort of relationship?
I liked it. I thought that it makes narrative sense to relate the Borg's end to the Borg's beginning. And I loved how the Borg Collective was born as a result of existential pain and longing, of the desperate desire to avoid accepting one's own mortality, rather than out of some bullshit sci-fi parable about fearing technological and social change or what-have-you. The Borg were born in terror and horror and desperate, desperate loneliness, not a sociology textbook. Love it.
The problem would be trying to locate exactly where the Borg were and perhaps trying to find where their origins lie, rather than going all out in some epic war that ends with a deus ex machina.
Except that it's not a deus ex machina -- not exactly, anyway. The Caeliar do not arbitrarily intervene at the last minute after having never been involved in the story before (which is part of the key definition of a DEM); they were a substantial part of the story from the beginning. That's not a deus ex machina, that's Chekhov's Gun. And, further, the Caeliar didn't exactly save the day by themselves --
Hernandez saved the day, by spreading Human/Federation values to the Caeliar, saving them even as she was also saving the Federation.
The end of the Borg was, really, a matter of everything coming full circle -- the Caeliar having to confront their own mortality and cultural stagnancy; the Federation having to confront its final choice between morality and survival, and being saved by its choice of morality; the Borg being forced to accept its own mortality and to relinquish its grasp on its slaves. So much of
Destiny is about having to accept your mortality rather than live in denial of it; I love it.