The universe of Star Wars has expanded beyond measure, or even expectations. Even considering the cinematic nonology alone — and excluding the vast library of canonical literature in the form of novels, comic books, video games — it still remains an exhaustive and thrilling narrative.
A new addition to the Skywalker dynasty is Ben Solo, the son of Han and Leia, who turns to the Dark Side for the same reasons as his grandfather: the promise of finding a space for himself, as one who feels as much darkness in him as there is light. Nevertheless, the man who becomes Kylo Ren has not exactly been faithful to the role constructed for him (in many ways).
His Fetal Force Powers
Being the grandson of the Chosen One, Ben Solo is capable of terrifying Force feats, but it seems that his powers start developing prenatally — Darth Vader once heard his voice saying "let the past die" long before Han and Leia meet each other.
Furthermore, Ben's harmony (or disharmony) with the Force was perceived by his mother while in the womb, which is honestly a little too early for most practitioners. For instance, both Anakin and Luke are only able to employ telepathy and telekinesis much later in life.
His Victory Over Luke Skywalker
Once Luke identifies a "darkness" flourishing within his young padawan, he plans to challenge him about its source. Upon observing that Snoke had already managed to get Ben in his evil grasp, he briefly considers murdering his nephew, partially drawing his lightsaber.
Luke holds himself back, but unfortunately the sleepy Ben mistakes his uncle's stance as an attack, and counters with his own. When this fails, Ben brings the entire cabin down on them, and leaves believing that Luke was dead. Although untrue, the very fact that he was able to defeat/escape the greatest Jedi with a single move is not exactly credible.
His Relationship With Snoke
The main reason that Ben turns to the Dark Side is his family's refusal to tell him about his ancestry, specifically about Darth Vader. His youthful disorientation is what allows the mysterious Snoke to convert him via telepathic linkage.
At this point, nobody knows that the Sith Lord is actually an invention of an older, more powerful one, but Ben is swayed far too easily by his charm and promises, nevertheless. If nothing else, Leia's bond with her son should have helped her figure out what was going on in his confused mind.
His Fascination With Grandpa
As he derives most of his strength through rage and betrayal, Ben Solo gradually transforms into Kylo Ren, Sith-esque Warlord (under the creepy guidance of his new mentor.) However, he discovers that his grandfather was both the Chosen One and the previous Sith Lord when Leia's political rivals leak the information.
From this point, he blindly worships Darth Vader, even placing his destroyed helmet on a literal pedestal. In fact, many people, including Snoke, Leia and Rey, try to convince him that he is his own person, but Kylo is not capable of letting go of his legacy for some baffling reason.
His Defeat By Rey
In The Force Awakens' final fight, Kylo initially bests Rey's lightsaber techniques and general Force-usage, almost crushing her under the weight of his experience. He attempts to draw her over to his side, saying that he would be her trainer (and teach her how to control the full spectrum of the Force.
Rey's epiphany notwithstanding, there is no logical reason why she could instantly turn the tides in her favor, succeeding in pushing Kylo away and marking his face with her lightsaber. Snoke taught him better than that.
His Cold-Hearted Patricide
Ben Solo loves his parents very much; even after his ungainly metamorphosis. For most of the time, he just avoided Han and Leia in order to keep his emotions under check, but this is not possible when his father accosts him (begging him to return to them.)
After an emotional exchange, Kylo Ren asks his father for help in ending his inner turbulence, and then just murders him. A smart man in so many ways, he is inexplicably incapable of seeing how this act could possibly make things better. And obviously it does just the opposite.
His Inconsistent Morals
Kylo Ren is eternally torn between the Dark and the Light — often jumping from one extreme morality to another, but he generally just remains suspended in an uncomfortable gray area. He kills his father, then saves Rey from Snoke, then expects her to become co-tyrant with him, then tries to kill her again, then changes his stance for the nth time.
The question is not why he cannot take a side and stick with it, but how this inconsistency begins in the first place. It's nothing but a cop-out if it all boils down to inheriting his grandfather's own sense of conflict. Give Kylo his own story!
His Failed Attempt At Matricide
Now that he has the blood of one parent on his hands, why does he not kill his mother when he has the chance? Kylo's finger lies on the trigger for a few moments as the scene switches between him and Leia, but he refuses to press it at the end. His inaction has no consequence, as she gets blasted out of the ship anyway by his accompanying wingmen.
Now, if he wanted her to die, he could have done it by himself; but if he didn't, he could have at least tried to save her? Or did he just not want to be responsible for Leia's death as well?
His Pants
Now, this scene is magnificent (because Adam Driver is magnificent), but that doesn't mean Kylo has to wear his pants at that ridiculous height. He clearly spends so much time meticulously manipulating his hair to perfection, dons a stylish helmet that is honestly a massive aesthetic upgrade over Darth Vader's, and that cape-belt-cowl combo is quite the fashion moment.
And yet, the man walks around in his private chambers with trousers jacked up almost all the way to his nipples. It's definitely a baffling stylistic choice.
Whatever Happens Between Him And Rey
Kylo Ren and Rey are one with the Force: a dyad that appears once every unknown period of time that are treated as a single living entity (?) Nobody knows why or how this happens, nor how the members of a dyad are selected. Is it random? Does it arise from a specific manifestation of some obscure Force-related event (like the Midichlorians)?
Or, are dyads formed between people who share some kind of heritage, like Rey and Kylo being Palpatine's and Darth Vader's grandchildren, respectively? So many questions.