I'd never heard of George Gissing before I picked up this book (I'm piggybacking onto a Victorian fin de siécle class), and even then, I assumed the George in the author's name was a pseudonym like George Eliot or George Sand (both women writers). Even though he's not a woman, Gissing is able to write about women in a way that surprised me.
When I finished the book, I originally thought he had done a better job of portraying the women than the men, but after listening to others talk in the class, I realized his men were more complex than I had perhaps at first given them credit for being. Although I still think his women were better characterized (mostly because they get all the interesting plot lines), the gap between how men and women are portrayed in the novel is smaller than I thought at first.
The Introduction of the critical edition that I read describes it as "the novel most fundamentally attuned to late Victorian culture and to the social issues defining that culture" because of its attention to detail (geography, willingness to describe vice) and its depiction of the issues facing women.
Odd Women in the title refers to the excess number of middle class women who had no hope of marrying, hence 'odd' not paired. This was in part due to emigration of men to the colonies, attrition through war, and the variable birth rate of men and women, but in the novel it meant that these women, who traditionally depended on men to support them, were often left in extreme poverty. The book not only discusses marriage, but the training of these odd women for work (other than the badly paid and overdemanded governess and nurse positions). It also presents arguments both for an against the idea of free unions (common-law marriage) which was beginning to emerge during the period, though usually not with favor.