Getting Biblical in Daily Life
Jewish Perspective
Esther (or "The Megillah" or "Scroll" as it is known in Jewish tradition) is apparently the first book in the Bible in which the word "Jew" is used to describe the Hebrews. Just by doing that, Esther marks a pretty big linguistic milestone in the Bible for the Jewish people. And it's important well beyond that contribution, as well, helping to shape Jewish cultural life and tradition in other ways.
Esther's biggest contribution to Jewish tradition probably lies in establishing Purim as a holiday. In fact, some liberal Jews see that as being the purpose of Esther. While the story might not be historical fact, it serves to help give the holiday a historical meaning, helping it to make sense. (Source.)
Jews with a more Orthodox or mystical perspective tend to see the book as being both historical fact and allegory—it really happened and it contains symbolic meanings. For example, one of the commentators claimed that the reason Esther's name is mentioned 52 times in the Book of Esther and the reason Haman's name is mentioned 52 times is to indicate that there is always an equal balance of good and evil in the world. Such readers also tend to look for the secret evidence of God's presence in the story.
(This collection of comments from various rabbis and sages could help to give you a better idea of how Jewish interpreters found various symbols and signs hidden inside the book.)
Christian Perspective
The Christian tradition as a whole has often been pretty skeptical about the Book of Esther. Since the book doesn't mention God or deal with any events that can particularly be interpreted in light of the life of Jesus (unless you see Esther as, in a weird way, a sort of forerunner to Christ since she saves God's people), it's frequently been left on the backburner. The Early Fathers of the Christian Church had virtually nothing to say about it, and when people in the Middle Ages commented on it, they usually tended to view it as an allegory instead of a historically useful or accurate tale.
The man who started the Protestant Reformation, Martin Luther, pretty intensely objected to the Book of Esther. This might be because it failed to mention God, or because Luther (who was very anti-Semitic and the author of a pamphlet entitled "On the Jews and Their Lies") didn't like the way it portrayed and celebrated Jewish national identity in relation to incompetent Gentile kings. (It might be for both of those reasons.)
Luther also said the book had "too many heathen unnaturalities." And John Calvin, the other major Protestant poobah, never included Esther in the commentaries he wrote on the Bible, only mentioning it once in his biggest religious work, the Institutes of the Christian Religion.
But some modern day Christians have started to take a more positive attitude toward the book. Like Jewish readers, they've decided to look for God's work hidden behind the scenes, arguing that there's a divine plan lying behind the events of the book. Moreover, figures from the Eastern Orthodox Church and some of the early Church Fathers actually did like the Book of Esther, since they read it in its altered form in Greek, which added six chapters of God-heavy material. (Source.)