This episode major significance is that it introduces the Borg. The Borg, half humanoid half machine, the species that in my humble opinion helped save a struggling show and fandom. The one thing Star Trek TNG lacked up to this point was a strong enemy. And the Borg became that enemy. So much so that they spanned two other shows. (Three if you count Enterprise), as well as being the major plot point of one of the many star trek movies.
The Borg were major plot points in some of my favorite episodes of TNG, which include the must talked about “Best of Both Worlds” two parter as well as “I, Borg.” On DS9 Benjamin Sisco’s wife was killed during well….the Best of Both Worlds. And On Voyager, the fourth installment of Star Trek was given new life when Seven of Nine was introduced.
It’s hard to imagine not having The Borg in the Star Trek universe, but this was the episode they were introduced. And it was Q who introduced the crew of the Enterprise and us to the species who would change the Star Trek Universe forever.