This novel features the first strong, independent black woman in a novel to search for her identity and happiness. In those respects, Janie is a very forward-thinking, powerful female protagonist, something relatively advanced for the time period in which the book was published. Although she is a victim again and again of male repression/domination, Janie stands up for herself at several points throughout the novel.
For example, after essentially being forced into marriage with Logan Killicks, Janie leaves him when Jody Starks comes along. This would be practically unheard of in the 1930's: a woman simply picking up and leaving her husband behind. But Janie is searching for her true self, and for her life partner, and she's not going to let any man stop her. However, she soon finds herself in a very similar situation with Jody. One might expect her to up and leave, just as she did with Logan. But you need to take cultural context into consideration: she is a woman, a black woman, who has no rights to speak of in this society. She imagined that her life with Joe would be free and easy, & to some extent it is. That is the financial aspect of the relationship. Joe is a successful man, and Janie reaps the material benefits of that success. But I think that as soon as Janie realizes what her life has become, & how much Joe hurts her/oppresses her, she stands up for herself. She tells him off, in a way that is purposely emasculating (making fun of his genitalia) in front of the other men, no less. After that, she doesn't let Joe tell her what to do or control her in any way. In fact, the power in the relationship shifts from him to her, and she proves herself a strong woman of the times.
She finds her equal in Tea-Cake, although some argue that this novel cannot be feminist, in that Tea-Cake hits her and controls her in much of the same way as her first two husbands. However, there is a difference there; Janie respects Tea-Cake as an equal, and he treats her as one (for the most part). Not to make excuses for the abuse, but there's a different tone in their time together as opposed to the first two journeys of Janie's life.
It's important not to judge Janie according to our contemporary standards of feminism. We must understand that any attempt to lead an independent life was a strong statement for women in the 1930's.