Many people hate the addition of Hayden because if, like me, you only watch the OT, Hayden comes out of nowhere, while we just met Sebastian as Anikin moments ago.
And it makes sense that he would return in the form he was redeemed in and, more importantly,
as someone Luke would recognize.
The Blu-rays fixed that. Now instead of appearing out of nowhere, his disembodied voice yells at Vader as Vader throws the Emperor down the chasm. Then, a few scenes later, you see him hanging out with Obi-Wan and Yoda. So it’s… wait, no, it’s actually even more incongruous, even if you recognize the yelling voice as that guy from Shattered Glass who somehow ended up on the Death Star and thinks it’s a good idea to scream at a pissed off Darth Vader, although I’ll admit he is smart enough to stay offscreen while he’s yelling.
But back on-topic, the Emperor change sucks too. But it only makes the scene worse, it doesn’t make the scene utterly incomprehensible.