If we are just looking at Curley's wife, I think we get a dynamic and sympathetic picture of the female plight in the lower classes of the agrarian west.
Curley's wife suffers from the strictures and the powerlessness of her position, facts of her character that are rather fully on display in the brief novel. Though she is certainly not a great person, she is represented in a way that lets the reader share her suffering.
I agree with my other illustrious e-colleagues in this issue. Do not be deceived by the way Curly's wife is presented. Yes, the men are unsympathetic to her and yes we never know her name and she is portrayed as rather a tart, and yet in some ways Curly's Wife is one of the most important characters in the novel because she sums up so many of the themes in the novel: loneliness, lost dreams and a need to belong with someone and somewhere. You might benefit from seeing to compare these themes and how they are displayed in other characters to get behind the apparent misogynistic attitude that Steinbeck displays.
I think the character of Curley's wife is a great example of how Steinbeck absolutely sympathizes with women. As Jamie pointed out, she is an abused woman without many options for escaping her future. She spends her time trying to communicate and relate to the common workers on the ranch, people she feels she may have more in common with. As readers, we are led to sympathize for her when we realize that the only people she can have a conversation with are the three "weak" ones she corners in Crooks's room. Unfortunately, she doesn't know how to converse with these people on an equal level, so when she is confronted by the men, she quickly threatens Crooks which effectively ends their conversation.
We as readers, and certainly Steinbeck, continue to feel sorry for her as a pawn in life when she seeks the attention of Lenny and is accidentally killed.
It is not the case that Steinbeck did not sympatize with women. In fact, he cared about them a great deal. Don't fall into the trap of confusing the writer with his work. In Of Mice and Men, Curley's wife is presented as she is, not how we would like her to be, or how we would like society to treat her.
Curley's wife is living with an abusive man. She lives in a world where men dominate and make all of the decisions. She is young, uneducated, and completely without a support system. She believes that the only thing she has of value is her sexuality. It will be her downfall, but the lack of respect for her as a woman and as a member of society will negatively impact the men in the story as well.
Although John Steinback might seem like a woman-hater. He shows the trouble of woman in the 1930s. They were proptery for most men and many men thought that a woman had only two roles: the Wh*re and The Mother.(the one who's fun and the one you can take home.)
The ranch men draft into the wh*re postion,simply because she wants to talk to someone other than less-than-stellar husband and her father-in-law. Curley's mother is never mentioned,so we could only think two things:she left or died. She has no fellow women to talk with. However, since she is a REAL person-she can't fit into the two extremes and is left dangling in the middle.