Sylvanas' goal? What does she want?

[Maarius]

Sylvanas is not evil. Pay attention to the cinematic.
"Ours is a cycle of hatred. We have paid the price for sharing this world and we have forgotten what makes us strong.". She's talking about bringing the Horde together as one and make them strong again. She cares about the Horde. Watch the cinematic where the Alliance begins to slaughter Orcs, she looks dismayed and once that immobilized troll gets stabbed by the spear she goes ape-shit which leads into the assault on the tower which her anger causes her to rally the Horde. Look in Saurfang's eyes. He's like "This is who we truly are."

from the prologue to "Before the Storm"

His decision to attack Theramore with a devastating mana bomb had the softer races wrestlin with their consciences. The only thing that had troubled Sylvanas about it had been the orc's timing.

speaks for itself

A curse upon Vol'jin and his loa. "I should have stayed in the shadows, where I could be effective without being interrogated. Where I could do as I truly wished."

hidden motivations

"Warchief," he said, "it is time. Your people await you."
Your people. No. Her people were back in the Undercity,

clearly not seeing the other members of the horde as her people

For her part, she did not have much interested in the Horde as a whole, although she took great pains never to let her true feelings show.

just doesn't care



although she says this...

She would have given me the Val'kyr for all eternity. None of my people would have ever died again." She paused. "I would have saved them."

... in the short story "Sylvanas Windrunner: Edge of Night" we can hear her thoughts:

The army of undead that surrounded and protected the Dark Lady was still hers, body and soul. But they were no longer arrows in her quiver, not anymore. They were a bulwark against the infinite. They were to be used wisely, and no fool orc would squander them while she still walked the world of the living.

So her Undead are just tools for her. Before her fall from Icecrown they were weapons, now they are her shield to help her staying in the world of the living and away from that terrible dark place she had seen before the Valkyr made a pact with her. She's just afraid of eternal damnation, so she needs her army as her shield.

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but I still don't think she'd be willing to mind-rape him into service like was done to her and the Forsaken.

I think she would do to Arthas corpse the same she did to Lord Godfrey:
.

[TheramoreIsTheBomb]

Fighting the opposite faction is not evil

[Soeroah]

1) To not die

2) To have her Forsaken not die

3) To be left alone

That's about it. But since this is Azeroth, being left alone isn't a realistic outcome in her eyes, so she takes measures she sees as being necessary to meet the other two goals.

[Deleted]

Sylvanas had an interesting story in Warcraft and maybe in WotLK, but since then Blizz has completely messed up the character. You cannot really ask for rational goals or motifs when it comes to Sylvanas because Blizz decided to write her crazy. Blizzard could have made her a convincing character: a former general suddenly finding herself in undeath. How does someone disciplined, hard-nosed and capable handle that? Instead they have her simply go mad and pointlessly trying to kill herself, her sister, thinking about killing her nephews, killing her former warchief and failing on all accounts.

As she is right now the character simply doesnt make sense.