Esther is one of the two books in the Bible in which God is not even mentioned (the other is the Song of Solomon).
Maybe that's why some Bible believers, such as Martin Luther, believed that it should be excluded from the Bible. In Luther's case, however, it probably had more to do with his extreme antisemitism. Because the point of the Book of Esther, if it has a point, is this: God loves Jews more than everyone else and anyone who has ever had a bad thought about them should be killed. (And Luther had lots of bad thoughts about Jews.)
There is a whole series of killings in Esther, all of them to avenge antisemitism. But since the Book of Esther does not mention God's name, it's difficult to blame him directly for these killings. Still, since Esther is included in the Bible, the God of the Bible must approve of the killings, insofar as a nonexistent being can approve of anything.
The Book of Esther also has an important message for women: your job in life is to look pretty and to please, honor, and obey men. If that means dancing naked in front of your husband's drunken guests, dance naked. Be an Esther, not a Vashti. (Which is, of course, bad advice. Vashti is the hero of the Book of Esther and she gets my vote for the best person in the Bible.)