In defence to those who found it puzzling that The Last Jedi didn’t give us more on The Force Awakens‘ Big Bad, I concede that we’re entitled to wonder whether Snoke was a Sith, and if so, how he fits into the always-two-there-are model. One might profitably muse on whether Sith-ness is in fact constrained to the always-two-there-are model, or whether that was just a story Plagueis/Palpatine, Palpatine/Dooku, then Palpatine/Vader told to make themselves feel special.
What I don’t concede is that the film has to explore that. I rather think we’ll have more fun speculating on such things ourselves that we would get from being told the what The Answer is. Because whatever The Answer turns out to be, the only possible response will be “oh”.
What’s much more important than Snoke’s origin/identity is Kylo Ren’s journey. Some may ask questions like:
If Snoke is a Sith, is Kylo Ren his apprentice? Or has Ren independently decided to revive Granddad’s cult? If Ren doesn’t see himself as the continuation of the Sith, in what sense does he think he’s the new Darth Vader? (But why hasn’t he taken on the title Darth?)
I think the defining characteristic of Kylo Ren is that he doesn’t know what the heck he’s doing. He pretty explicitly started out as a Vader fanboy (“I will finish what you started, grandfather”), just like any other edgy teen who is drawn to big-R Romantic notions of darkness. The only difference is that instead of sublimating this into making a collection of Judas Priest LPs, Ben Solo has enough innate Force ability to parlay his really slightly laughable obsession into something genuinely dangerous.
Subsequently, he is obviously fascinated by the idea of turning away from this path to return to Han — both compelled and repelled — but in the end he is too much in fear or in awe of Snoke to do it. Yet when the chance comes, he kills Snoke in a completely unpremeditated moment. He’s thinking with his hormones, not his brain — by which I don’t just mean whatever kind of affection he has for Rey, but more broadly the whole wash of mutually confusing and contradictory adolescent hormones. At any moment, he could go either way — as when, immediately after Snoke’s death, he and Rey fight joyously side by side, only for the moment of camaraderie to dissolve the moment the Red Guards are defeated.
Ben Solo is a kid who is fascinated by Nazi memorabilia, first excited then horrified to find he actually has it in him to create a Fourth Reich, and now winging it from moment to moment.
Isn’t all of this tremendously more interesting than one more This Is Your Destiny journey?