Re: Anyone else think they should have left the Borg well enough alone
And frankly, if the only way to keep an enemy intimidating and fearsome is to keep them "Mysterious" they're a lamely thought-out enemy.
The Borg are a monster, not a villain. Villains are like Cardasssians, Romulans and Klingons - complex societies that can be just as diverse and interesting as the good guys. They are "real" characters who become more interesting the more you explore them.
Monsters are forces of nature that represent some primal fear. They aren't "real" characters so they become less interesting the more you explore them. The Borg are an example of this type.
There is a place in
Star Trek for both villains and monsters, but they require different approaches. The biggest difference is that monsters cannot tolerate exposure the way villains do.
Instead, spare the monsters and make more direct use of your villains. Here's an example of how to do that: if the Borg are a threat to everyone in the galaxy, perhaps the villain characters (Romulans for example since this maneuver would be beneath the dignity of the Klingons to attempt) divert the Borg from their own regions of space towards the Federation. Then the story is really about Feds vs Rommies, with the Borg hanging back as the looming, unseen threat.
I think they ruined the Borg adding the Queen. They were much more menacing without a single mind behind, but as a pure hive. Now it's just a slave race with some ambitious lady at the helm. Without her they would be more of a mystery and harder to understand.
That's not what the Queen is. The Queen is the representation of the entire single hive mind. She IS the Borg. All the billion Borg drones form one single individual.
Then they misrepresented the Queen badly. She should have been emotionless and completely, terrifyingly self-contained, with a remorseless drive towards greater perfection through assimilation, instead of a scheming minx-type dominatrix who wriggled around and drooled all over poor Data. I really can't envision the entire Borg Collective like
that!

The sexual aspects alone rendered the character comic, and to think of the whole Borg Collective in those terms is downright hysterical.
There are undeniably sexual aspects to assimilation, but to start making them obtrusive and literal turns them into gross comedy. Just another way in which the Borg are very delicate, like all Monsters, and easily misused by poorly thought out writing.
All I'm really saying is "They're determined to enslave the whole human race!" is setting the bar a little high. It doesn't need to be that epic, "They will invariably try to assimilate anything more sophisticated than a garbage scow" would accomplish a good amount of menace without the need of "unleashing" the monster.
If the Borg will just attack whatever's right in front of it, a la the Doomsday Machine, and have no will to selectively go after humans or Ferengi or whatever, then that's a good way to keep them from being too powerful for it to be plausible they wouldn't take over the galaxy right away. Then it becomes a game of each society in the galaxy trying to divert the Borg to their foes - that could be an interestingly nasty little game in which the Borg are the threat, but not really the ones driving the story.
Another idea: what if Founders are the only beings in the galaxy that the Borg can't assimilate, and the Feds have an iffy relationship with the Founders? Extend the Dominion's immunity this way: when the Founders find Borg on their boarders, they institute a policy of immediately killing any Jem or Vorta who is assimilated by remote control (via whatever tech you like) so that the Dominion's military and command structure is immune to the Borg. That complicates things for all Alpha Quadrant powers!