Agnes Grey contains equally fine writing to both Emily's and Charlotte's work with a storyline that fits in between Jane Eyre and Wuthering Height in terms of likeability.
It is, like Jane Eyre, the tale of a governess. Yet, unlike Jane Eyre, Agnes Grey focuses on the problems faced by a governess in two different families. One family full of young children who are ungovernable and the other a family of older children, the girls of which play on the local men's heartstrings or act in unladylike ways.
The slight problem I had with this novel compared to Jane Eyre is that the protagonist appeared to be an all holy women compared to all other people around her. In Jane Eyre it was clear to see that Jane had her faults (including an aggressive temperament) however it is less clear in Agnes Grey which makes her a less likeable heroine and more unrealistic character.
That said it is thoroughly worth reading this book as it is a worthy classic and provides a balance between the work of the three Bronte sisters in terms of style, tone and depth.