I assume Skin of Evil entirely because it explains the sudden disappearance of Tasha Yar? Because otherwise, that episode ranks up with Sub Rosa.
Yes. Oh, shoot, do I need to include The Naked Now to explain the Data/Tasha thing?
Edit: Also, I suddenly have this irrational desire to go back and watch TNG straight through. I don't have the time, of course...
How is that irrational?
The one before Skin of Evil is actually quite funny, because I think it was shot after it and in it Tasha waves to the audience in the background to say goodbye.
Also, originally Denise Crosby (who ended up playing Tasha) had auditioned for the role of Deanna Troi while Marina Sirtis auditioned for Tasha. I'm glad they switched them around.
Brent Spiner is just fantastic as Data, it must be a hell of a role to play. His maniacal laugh as his evil self or evil twin is so great.
Picard is my favorite captain, maybe because he never became admiral.