These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
And there are fans who just don't think she's as interesting as Chocolat.
Broken Base: The series' social commentary about love and femininity is seen as either thought-provoking and adding depth to the story or clumsily written and making it incomprehensible to non-Japanese audiences.
Should Chocolat or Vanilla have won in the end?
Designated Hero: Though the protagonists are certainly not as villainous as the Ogres, their habit of harvesting human emotions for energy sounds like an evil plot straight out of Sailor Moon, though it doesn't seem to harm them.
Evil Is Sexy: Well, sexier anyway. After becoming the Ogre Princess, Vanilla sports an elegant evening gown when transformed into witch mode.
Values Dissonance: A lot of fans in the west (where tomboyish girls are seen as more desirable) don't see anything wrong with Chocolat's behavior early in the manga, and think she's treated way too harshly. This may be the reason why it never really took off outside Japan (except in Italy of course).
The Woobie: Both Chocolat and Vanilla can be this.