It's surprising how TCW even managed to worsen Ventress, a character who even by the standards of the old EU barely managed to be more than remarkable. And it was the obvious favoritism she held in contrast to Dooku and Grievous what ruined her for me.
The show doesn't stop portraying her as a bloodthirsty, pushy femme fatale who loses every fight she gets in, until she decides to cut all ties with Dooku and the CIS, and it's at that point when the show does a 180º turn on her character.
All of her sins and missdeeds automatically are forgiven, with the writers expecting the viewer to find her actions justifibale by giving her a bunch of tear jerking moments and a barely concise backstory that does as much as to explain her motivations and turn to the dark side as the prequels did to Anakin's character.
She gets to hang out with Obi Wan, she gets to hang out with Ahsoka, she gets her own love interest and ultimately, she is turned into a martyr. The show makes her out to be as someone just as important as Grievous or Dooku, and yet, the story would have go on perfectly without her involvement at all.
But truly, if there is a thing which I will never be able to forgive Ventress for is that she, along with the rest of the Nightsisters, is a fucking Greyfag.