Sauron is going to show some genuine repentance at the end of War of Wrath. Sauron after serving under Morgoth so long seems to have a fear of punishment. After his defeat to Luthien, he runs and hides, because he is scared of what Morgoth will do to him. He hides and refuses to return to Valinor due to what Morgoth will do to him.
He can increasingly become cruel and vicious to his enemies, but he could still feel he is doing it for a greater good. His enemies deserve the cruel fates, because they are against the progress of the world. Secondly fear will stop others from opposing him.
I always thought there could be a bit of the mad scientist in Sauron. He is so keen to improve creatures, he performs disgusting abhorrent magical/scientific experiments on them such as the with werewolves (as the host have outlined.)
I think even when forging the Rings of Power, he should not have completely been broken. I think the moment he snaps is when he narrowly escapes with his life in the Battle of Gwathlo. That could be a moment, where his hatred overpowers him and rather than control and better the world, he wants to be God and destroy the Elves/Numenoreans.