The Borg as they originally appeared, infinitely adaptable and nigh invincible, had potential. Trek writers deciding they had written a villain that was too mighty and suddenly pulling an endless series of technobabble macguffins out of their nether regions rather ruined that.

They honestly would have been best left to the 'Here Be Dragons' regions of space, a warning to travelers to take care where they tread (rather how it seemed Q intended the meeting with them to be) rather than seasonally recurring villains suffering from serious decay.

>TNG was generally pretty shit at villains. Q, the Borg, the Ferengi
>(remember when they were going to be the biggest galactic threat since
>the Klingons?), that Romulan Stasi nonsense, Counselor Troi's
>mother...
>

Be fair, Lwaxana Troi was utterly terrifying... to Capt. Picard :)