Ever since I had to write a Bat-Mitzvah project on a biblical woman, I've been convinced that Vashti was hard-done-by by the commentators over the years. I've always thought that the text in no way showed her to be a bad person -- on the contrary -- and disliked the way she's been victimized.
Over the past few weeks, while we've been reading the first parashot of Bereshit, I've been surprised to discover that my husband's family has their own hard-done-by biblical character: Esav. My husband's father, z"l, even went so far as to establish a (joke) Esau Rehabilitation Society.
For a very interesting take on this, see Rabbi Ya'akov Meidan, who argues that Esav, who refrained from killing Ya'akov out of respect to his father (Bereshit 27:41), was greater than Ya'akov's children who allowed themselves to sell Yosef despite their father's love for him. Rebecca, argues Rav Meidan, sent Ya'akov on twenty years worth of exile for nothing; Esav would never have broken his father's heart by killing Ya'akov, however much he was tempted.
In a further article (a reply to Rav Moshe Lichtenstein's objections to his initial piece), he emphasises that because of his deeds, Esav was certainly still more evil than good. However, he got so many 'points' for his enormous Kibbud Av, that according to Midrash Raba he merited to have his head buried in Ma'arat Hamachpelah.
It has also been pointed out that if you read the verse in which Esav gives up his birthright literally ("Behold, I am about to die. What good is the birthright to me?"), perhaps it's not so hard to understand why he would do it; was he, perhaps, literally returning from the field starving, or perhaps wounded?
In addition, the Midrash makes several connections between Esav and King David (both redheads, for example; the Midrash says that when Shmuel first saw David, he initially thought he looked like Esav).
All in all, the case isn't as strong as it is for Vashti; but it's interesting to note how few biblical characters are ever black-and-white.