1. Conspiracy
Something is rotten in Starfleet and it turns out to be a man who is full of these horrible insect things that are planning something nasty. This episode has a great setup for later years which is, sadly, never followed up on. I never quite got why, since one would have imagined it would have made for a more interesting storyline than, say, Lore teaming up with the Borg, or endless Klingon soap operas. Still the episode itself stands up well as a bit of great tension, suspense and a nicely gory set of visuals. If all of TNGs first season had been like this, this would have been a very different list.