The thing about Crossovers is they can be jarring to the mindset of a reader. Especially, when the reality of this story lent to it through the use and eyes of the Lower Decks personnel grounded it more so than other stories might at times be.
I apologize for failing to warn you about the crossover part, I'm sorry about that. Well, yes, the story is still focused on Lower Decks personnel, and one where they just might save the day and prove pivotal. That's just one of the many elements of this fic.
If things get too hairy, here's my Star Trek: Expanded Universe wiki entry on this fic: Dark Realm