There was nothing exactly wrong with the Queen idea, and she worked OK in First Contact - but then she started appearing in every Borg episode in later Voyager, and suddenly it wasn't the Borg themselves that were the threat, it was just the queen, and her drones were basically mindless footsoldiers for our heroes to hack and slash their way through.
This is a good point. I liked the Borg best when they were a faceless, homogenous, unreasonable force.
There are ways to rationalize the Queen away as a literal queen for the most part. I think the greater factor that diminished the Borg was that they seemed like pushovers. Tiny little Voyager escaping them every week? Riiight.
Another point I agree with. I see the Borg Queen as less of a literal queen and more a focul point of Borg consciousness; an interface. I'm not easy with the idea of a figurehead for the Borg. Although, after having said that, thinking about hives, hive creatures here on earth do have a queen. For some reason I can go with it in First Contact the movie and less so in Voyager.