There are many problems (OK, call them "issues") with the book of Esther.
The biggie? God is never mentioned in the book.
But I wonder if Esther 8.17 is a clue to the meaning and purpose of the book. (I'm uncomfortable with those who make blanket judgements against this -- or other -- books that have traditionally been considered canonical. I generally go with the idea that it's safer not to mess with the traditions of the church, and this is one of those areas where antiquity gets the deciding vote).
But here's 8.17: "And in every province, and in every city, whithersoever the king's commandment and his decree came, the Jews had joy and gladness, a feast and a good day. And many of the people of the land became Jews; for the fear of the Jews fell upon them."
Is Esther -- like Jonah -- ultimately a book about evangelism?