Re: List of essential episodes.
The Borg - Q, Who?
Species 8472 - Scorpion
Dreams; hallucinations; illusions - Unimatrix Zero
Q - Encounter at Farpoint
/Hide and Q
/All Good Things...
Eugenics/Augments - Space Seed
/Star Trek II: The Wrath of Khan
Mirror universe - Mirror, Mirror
/In a Mirror, Darkly
Time-travel - Tomorrow is Yesterday
/City on the Edge of Forever
Nazis - Zero Hour
Dominion War - In the Pale Moonlight
/The Siege of AR-558
"...the most elementary and valuable statement in science, the beginning of wisdom, is I do not know." - Lt. Commander Data, "Where Silence Has Lease"