Whenever they show up, it's always that usual Big Voice saying "Resistance is futile" over and over and over. And TNG established that the Borg are vastly faster so you can't run from them, and they become invulnerable to your weaponry after one or two shots (and those one/two shots are never enough to destroy a Borg ship) meaning you can't destroy them without a plot contrivance.
So, to wit, you have an enemy that you can never have interesting interactions with since it's always just that same Voice saying the same thing over and over, you can't beat them with weapons, and you can't run or hide successfully since the Borg never lose interest and just leave after a while.
They also outnumber you 100:1.
All in all, you've created a Boring Invincible Enemy (
http://tvtropes.org/pmwiki/pmwiki.php/Main/GenericDoomsdayVillain?from=Main.BoringInvincibleVillain), or a Villain Sue (
http://tvtropes.org/pmwiki/pmwiki.php/Main/VillainSue). Neither of which are something you keep around.
Plus, for anyone who says "Just think outside the box", TNG already exhausted that. Hack into the Collective mind and trigger some plot contrivance? They did that in BOBW meaning you can never do something like that again. Use a natural phenomenon like a Solar Flare? TNG did that too meaning you can't use THAT again either, like teleporting them into a Black Hole.
All together, VERY boring enemy. Just kill them in some fashion, be rid of them, learn the lesson of how NOT to make an adversary from them and apply that to any future foes.