You'd best settle in with "Datalore," since it's the last episode you really need to see from the first season of Next Generation until the last few.
It's a good way to go, though! In case the title doesn't give you any ideas, let me cut it a little short: Lore. Lore, as in Data's evil brother.
Now, in the off chance that you're not at all familiar with Next Generation, Data, or much less Lore, let me just say that if it had only been the one episode, "evil brother" could very well have been an unfortunate gimmick, even if the rest of the episode remains pretty fascinating, because there's more that you need to gleam from "Datalore" besides Lore.
(And I'm not even referring to "Shut up, Wesley!")
The episode also establishes the Crystalline Entity. This is one of the more ambitious and mysterious alien lifeforms ever conceived in Star Trek (and would be seen again to greater effect in "Silicone Avatar"), a faceless being of apparent sheer destruction, perhaps like rogue probes in "Changeling" as well as The Motion Picture and The Voyage Home, and perhaps the best example of what Q was hoping Picard would figure out in Next Generation following the trial begun in the pilot and ended in the finale.
Note to anyone who cares: if you were interested in retelling the story of Data, it would be absolutely essential to include the Crystalline Entity.
There's plenty of Data's story in "Datalore," including his specific origins. The funny thing about Data was that even though there were androids running around the original series, including dubious "followers" of the nefarious Harry Mudd (imagine if they made a movie out of him!), Starfleet treats Data as pretty unique thanks to his intricate programming and abilities. Also because until "Datalore" he's believed to be unique. Turns out there was at least one other model executed by his creator, one that didn't suffer from the same social setbacks and therefore proven very meddlesome (and that's before Lore unleashes the Crystalline Entity that wiped out all life on the colony where Data was later rediscovered).
There's plenty of fascinating material to be found here, but I hesitate to give it the full rating because, well, it's basically a pretty clear offering from the first, imperfect season. Thank the creators that it exists and possibly move along. Yes, Wesley is the only one who seems to notice that Lore tries to replace Data, and hears "Shut up!" twice during the episode for his efforts, which is yet another indication that the writers are either themselves aware that the character has already proven more annoying than they'd intended, or they keep inadvertently feeding the audience the reaction they eventually get.
And yes, it's an "evil twin" episode. Still, by all accounts a quite noteworthy one.
franchise * series * essential * character
Memory Alpha summary.