The Borg were at their freakiest in the episodes "Q-Who?" and "Best of Both Worlds I & II". After that they -- for me -- they lost their mystique.
Then they kind of reclaimed it for First Contact, but they were still not as scary as they were in those first three episodes.
I think Hugh really did a lot to kill them for me.
Agreed. But what made them especially scary was the music in "Q Who?" and especially "BOBW"; it made your skin crawl!