Arthas
Oh, right. Kerrigan and Raynor. (Starcraft)
Raynor's resilience in the face of repeated loses, his first insistence that Kerrigan isn't nothing but a monster, and then his final decree that he will be the one to kill her after she kills his friend Fenix, because he finally realizes she IS nothing more than a monster at this point.
Kerrigan, on the other hand, goes through a betrayal by her lord that leads to her capture and assimilation by the Zerg. Following the destruction of the Overmind at the Hands of Raynor and Tassadar, she regains her free will... but has discovered she enjoys the power. Manipulating her old friends, convincing them she isn't a monster anymore, she gets them to do her dirty work... until such time as she find them no longer useful. Brutally backstabbing them and killing Mengsk's second in command, Duke, Mengsk (the lord who originally betrayed her to the Zerg when she was human) patches in and berates her for being a murdering bitch. She laughs off his attacks, pointing out that HE was the one who created her, and as such, deserves what he gets. (Not to mention Mengsk is a total fuckwad besides.)
However, upon her slaying of Fenix, she isn't quite so ready to defend herself against Raynor's final loss of belief in her; though she mocks Raynor's decree that he will be the one to kill her (Big words, cowboy, they don't suit you) Raynor remains resolute.
His words, after all, do seem to have an effect on her. At the mission's end, given an option to slaughter the rest of the forces she has at her mercy, she declines, stating that, oddly, for the first time, she tires of the killing.
Looking forward to how these two are developed in SC2. Most likely, since they are popular, their flawed and interesting dynamic characters will give way to larger than life cliches.
But for now, at least, they are surprisingly well rounded characters.
So well received, in fact, that Blizzard decided to do the exact same fucking character arc again, only this time, instead of a badass ninja assassin, they turned a whiny spoiled prince paladin into a whiny spoiled prince death knight.
Then they turned him into a walking cliche. Which honestly is a step up from what he was.