Overall, the story felt lackluster. Maybe because Countdown had an epic feel to it and this prequel didn't.
I suspect that Mike Johnson and Roberto Orci weren't aiming for "epic." Countdown to Darkness
always read to me as the next story arc in the ongoing series. CtD
has as much in common with "A Private Little War" as "The Truth About Tribbles" had in common with "The Trouble With Tribbles" or the Mirror Universe storyline had in common with "Mirror, Mirror" -- which is to say that IDW has progressed far beyond rewriting original series episodes and is instead taking ideas and concepts and giving them a wholly unique spin in the film's continuity. IDW probably recognized (quite correctly) that they would get higher sales (and more buzz) if they packaged this storyline as something else, something separate.