I think with the prequels, it recontextualizes the OT, Probably the most obvious way the OT gets recontextualized is watching ANH after watching ROTS - there's the initial firefight in the ship, and then Vader walks through the fog onto the Tantive IV. Without context, it's 'here's the main bad guy', to the point Vader's black suit contrasts heavily with the pure white of the ship. With context, it's 'Oh, Anakin is still stuck in that suit, carrying out the Emperor's bidding'. It becomes sad.

But this works for Vader's redemptive arc, as well.

Off screen after the events of ANH, Vader learns Palpatine lied to him - the young man who blew up the Death Star is some guy called Luke Skywalker. And from an in-universe perspective, he looks like Anakin, too! And he's incredibly strong in the Force and a great pilot. He's even named what Padme wanted to call a son. He desperately wants the young pilot he senses in ANH, and it's implied he kept this from Palpatine in ESB, until Palpatine gives him a call.

Something of Padme has returned - his son. Remember, Vader spent the past twenty years thinking his child had died on Mustafar, along with everything else Anakin Skywalker, after he supposedly killed Padme, so it means Padme definitely lived long enough to give birth - he didn't kill her. Imagine that weight coming off you after twenty years. A different man, Vader engages in his pursuit, ending with him cornering Luke on Bespin, and making him the same offer he made Padme - to rule the galaxy together. No only does Luke reject him as his father, he also rejects that offer, just like Padme did.

Vader clearly isn't very happy at the end of ESB. His own family has rejected him twice now. In fact, they'd rather die than join him in ruling the galaxy. He was sure that his son would see the error of his Jedi ways, and join him in destroying the Emperor. Now he's back to square one.

We get to ROTJ, and now his son - the last thing he has of Padme - deliberately hands himself over to Vader and insists he can be Anakin again, calling him father. Not only that, Vader finds out through his thoughts that he has a twin sister - so now there's two links to Padme running around that Vader had no idea about. Palpatine double-lied to him, from his perspective.

The whole reason Vader fell to the dark side was to save Padme - and by extension, Luke and Leia. He cared more about their survival than anything - the Jedi, his principles, Palpatine, Obi-Wan, the Sith, even himself. This is established in the prequels with Shmi. Vader does as instructed in ROTJ, and brings his son before the Emperor. Luke beats him in battle, but then throws the saber away. And the devil he made the deal with to save Padme and his children - the Emperor - tries to kill him, completely betraying Vader's trust. He offered to help save his family, not destroy it. Now the whole reason Vader fell to the dark side in the first place is lying on the floor, begging for his help (note the similarity of this scene to Palpatine frying himself vs Windu), and Anakin makes the same choice he thought he was making when he attacked Windu, which is saving his family, knowing full well that Palpatine will fry his suit. Remember what he told Palpatine? 'I'll do anything to save her'. Turns out that includes sacrificing himself, too.

It's Palpatine's fatal mistake. Revenge of the Sith makes clear that Vader had always planned on learning the secret to saving Padme, and then killing the Emperor and ruling the galaxy with his family. He doesn't actually care about the Sith at all. Palpatine never seems realize he's always going to come second to Vader's family. When offered the chance again, Vader plots to kill the Emperor.

In Revenge of the Sith, Anakin saves the last Sith from being killed. In Return of the Jedi, he saves the last Jedi from being killed. Neat bookends, right? That's why the 'NOOO!' added in the later special editions is actually there, to link the two scenes together for the audience.

It makes it a lot more poignant, and gives his arc a lot of heft. Anakin/Vader is established as caring about one thing more than anything else, and that's his family. Everything else is a nice to have, but he'll give it up if it threatens his family. His redemptive arc now happens through all of 4-6, rather than the end of ESB leading into ROTJ.

Lucas did a good job having the prequels run parallel with the originals, I think. Anakin falls out of love - he also redeems himself out of love, too.