Honestly, speaking as someone who's been here through every step of the First Splinter timeline and before that (I started reading the novels right around the time of the Invasion crossover, so 96ish)... I enjoyed Coda. Is it how I would have closed out the novelverse, the curtain call I'd have given the storylines and characters who've maintained this expansion of the Trek universe over the last twenty years? Probably not - it did feel a little sparse on non-TNG characters in roughly half of it, I do feel the novel original characters didn't get their due (what with Konya, Elfiki, and Trys all dying in the course of the first book, Bowers being the only significant original character in book two, and the only non-canon originating characters of note in the third being MU versions of canon characters, so while TECHNICALLY original, they don't quite fit the bill in my ranking), which really hurt with regards to the Titan crew, who really got underutilized, and, yeah, I'd have liked some indication that someone would subsequently remember what happened in resetting the stage for the "Prime" timeline, something tangible that says to someone in-universe "this happened and it mattered," rather than just leaving the audience with that awareness, rather than anyone in universe who knows the sacrifice made to allow all of it to continue.
Still, I enjoyed it. I mean, yes, if pressed, I would probably just call Collateral Damage the place where the novelverse ends in my heart, because it means that all the characters I love are still going off, still existing, having further adventures, even if that's not something that, by nature of tie-in material, would ever be depicted officially. Which, given the little continuity hiccups - not just Ranjea's appearance, or Hegol's miraculous recovery no one talks about, but also Kira's inner monologue at one point refers to the Kai as "he," when last I knew, the Kai was Kai Pralon, and no one talks about the Kai changing hands or Pralon transitioning - I honestly feel like there's room to, if desired, treat Coda as a splinter of the Novelverse, like how Wesley uses his Traveler abilities to touch the Rene's of other timelines, so there's acknowledgement that there are timelines where he does exist beyond the one presently under attack.
But for what Coda is, the Novelverse's curtain, I enjoyed it for that. Maybe it was caught up more in the message about how this timeline is giving way to the Prime version that it lost sight of its characters, but... I mean, that's not exactly new to the Star Trek experience, now is it? Star Trek has always been about messages, and, looking beyond my own full awareness of this as the end of the Novelverse, that there has to be an end to the continuing adventures that I've loved for years, and it was decided to offer a story that said that the sacrifice of this timeline is in service of the overriding canon... Honestly, I still see the optimism in that story, that message. Because what I'm taking away is a message that feels very Trekkian - act to protect, act to help, act to save lives, even if the people you're saving will never know of your efforts, even your sacrifices, because it's the right thing. That, fundamentally, the most important phrase in the universe is "let me help." That you do the right thing not for accolades but because it's right, because no one is watching, no one is judging you... except yourself. That these characters recognize the gravity of the threat facing them and decide to fight back, even knowing that, win or lose, they do not make it out.
In looking to conclude the novelverse, rather than leave it left uncertain, give it a clear finale that lets people walk away, to disembark this journey, because there's a different one that the books are mandated to adhere to (to strain my metaphor), the message I ultimately take away is that even if no one else knows, our actions, our choices matter.
"If nothing we do matters, then all that matters is what we do."