In my opinion this is the weakest of TNG's season-ending cliffhangers, though obviously I'm in the minority here.
The first problem, which other have noted, is that the Borg became nearly untouchable after "Best of Both Worlds". Once you've beaten an unbeatable foe, what is left to do? "I Borg" took a clever dodge; "Descent" does not.
Turning the Borg from soulless invincible foes into evil sadists is not a clever twist, nor is putting them under the tutelage of Lore (who, I suppose, is the #1 evil sadist in the galaxy). Making Data's first encounter with emotions a bad one is an intriguing concept, one that could have been good on its own (it generates some creepy scenes) but doesn't get its due here.
Not a total waste, but you get the feeling TNG was getting a little stale by this point - a feeling confirmed by the lackluster seventh season.