Force-ghost - the ability to pass on your wisdom and knowledge after death in very infrequent and inconvenient ways.
I think it's also a power that's denied to Sith because they are unable to make peace and become one with the Force. I think when Legacy Palpatine's final clone died, he was dragged into oblivion by all the spirits of all the Jedi who had ever lived.
I think, in keeping with the subtler side of the Light side of the Force is that you get little glimpses of something during Revenge of the Sith, where Yoda looks straight into Palpatine's eyes and the latter is briefly terrified. It's an interesting moment because specifically from that point on in the saga, Palpatine never regains the same control over events. He loses Yoda, and Vader is maimed, robbing him of his perfect apprentice, and his Empire suffers a slow drip of setbacks until his defeat. It's almost as though Yoda breaks through the veil and sees the whole future, which Palpatine himself can't access. I dunno, it's interesting, this idea that there's a bit more to the Light side than just a tech tree.
That's only in the new canon. In the old canon, Sith force ghosts haunt the tombs of Korriban. Some even incite wars or baptize new initiates to the cause. The Exar Kun War was fueled by two Dark Jedi that the Sith spirits supported.
There's also the fact that unlike Jedi ghosts, Sith ghosts can possess vessels and come back into the mortal realm. Lucas' favorite SW comic was Dark Empire, where Palpatine's spirit inhabited a series of clone bodies. He was finally foiled, not just by the Jedi, but by an Imperial deep state led by the Sith Lord Carnor Jax that enjoyed the freedom they experienced after Endor and didn't want to give it up to the revived Emperor. So they poisoned his clone bodies, forcing him to seek a vessel among the Skywalkers, which led to his doom. It is also notable that in that same comic, we see Palpatine commune with the spirits of the Ancient Sith when he was down to his last clone body, and they laugh at his failures.
In Jedi Academy, Marka Ragnos did the same after Tavion shot his tomb with enough Force energy; Ragnos possessed Tavion and fought with his sword, as if he were once again in the flesh. If it wasn't for the timely actions of Jaden Korr destroying Ragnos' staff, Ragnos would've ruled the Empire and led them to victory against the New Republic.
Revenge of the Sith is a tale of the Jedi's failure. They literally had every advantage dangled in front of their faces, and they failed to take note or use them. And even though Palpatine lost his perfect apprentice, he still gained a powerful one, and his hold over the galaxy was uncontested. He even tells Vader to let the surviving Jedi go, to let them bury their heads in shame in the backwater worlds of the Outer Rim, as payment for a thousand years of arrogance after they defeated the Sith the last time. Palpatine was more than happy with the development, especially since if Anakin retained his power, he'd have obviously killed Sidious and taken the throne.
Also, the Empire continued to go on long after its supposed defeat. Even before the Emperor returned in the flesh, the Empire's remnants, emboldened by Thrawn's adventures, seized Coruscant right before the Emperor returned.
It still feels like the Light Side is horribly underpowered. That's basically my biggest problem with both Lucas and Tolkien's works. The Dark Side gets all sorts of cool toys and powers, and the Light gets hippie magic bullshit and some one-with-nature crap. Which, if you look at the Bible and other religious texts, is the exact opposite; God who represents the supreme good has no problems throwing lightning storms, creating life out of nothing, raising people from the dead, etc.. The kind of power Anakin and Palpatine sought from the Dark Side would be the kind of power you'd usually see be associated with Divine powers. I mean, your average pleb back in the old days would interpret someone getting struck down by lightning as God or the gods getting angry with that person because he's somehow wicked.
Basically, the powers the Sith seek in the Dark Side are powers usually attributed to Divinity in most religions, whereas the powers the Jedi have with the Light, outside of basic telekinesis, buffs, and wielding a lightsaber, are the kind of hippie bullshit granola-bar nonsense that you'd expect from a new-age mystic who's trying to leave traditional religion because he wants to worship or be in harmony with nature or some crap. The only truly impressive power they have outside of telekinesis is mind tricks, which are more associated with quack mystics who try to pull a fast one on people. Not knights serving a higher power who enforce justice.
That's probably why, as a kid, I found more common cause with the Sith, because not only are their powers more similar to what usually passes for Divine powers in most religions, it's also because Jedi philosophy sounds like the same hippie yoga bullshit that new age people today try to pass off as religion, and while it has a smidge of Biblical precepts, like not giving into anger or temptation, or having faith in a higher power, the Jedi Code in the end preaches some kind of detachment that feels unhealthy, especially when they cast love as the enemy, when most moral systems cast love as something universally good.
Sure, the Sith are a bunch of backstabbing cunts, and that's something no good or Godly person would mimic, but at least the Sith don't cast love as the enemy the way the Jedi do, and they don't take it up the ass from a clearly corrupt government that just takes advantage of the Jedi while doing nothing but fattening the wallets of their richest and most privileged inner circles.
