The Nexus in GEN.
It was just too powerful.
You could travel anywhere in it by force of will.
You could go back and forward in time by force of will.
A bit of you remained around in it once you left it.
It gave you immortality.
It gave you the delusion you were experiencing your deepest wishes.
It made you want to stay in it.
I could understand it maybe if it were some sentient super thing like the Q or the Companion or the Guardian on COTEOF but it seemed to be some sort of natural phenomenom.
OK if you could travel in time why didn't Picard or Soran go back in time to before all their troubles began and make sure Soran and his family were off planet/ship when the Borg attacked or about a hundred other things that didn't involve destroying the ship...
Forget it. I could rant about this for days. Don't start me on Picard's or Kirk's greatest wishes.