All very different, but all brilliant.
Nana was brilliant in atmosphere: Zola describes the hot, odorous backstage of the Variétés in such a physical way that you can almost feel the sickly stuffiness. I also loved the way he contrasts the two worlds in Parisian society: the contrast between the Comtesse Muffat's icily respectable reception and the dinner organised by Nana is wonderful - the men are the same group of aristocrats, but the women are different, and the way that Nana tries to bring an air of elegance to her evening but only succeeds in producing a rather incongruously bourgeois atmosphere is wonderfully described. The last scene, in which Nana is dying in a hotel, surrounded not by the men she has lived off but the actresses and prostitutes she has competed against, is unforgettable: outside the crowds are calling 'To Berlin! To Berlin!' as the Franco-Prussian war begins and upstairs Nana is lying with her beauty destroyed, dying in the most disgusting and painful way.
L'éducation sentimentale also shows a French society which is divided between the respectable women and the underworld of prostitution, with men moving freely between the two, and is also a reflection of the perceived corrupt French society at the time, but more bitterly ironic and less tortured than Zola. It's a sort of Bildungsroman, but describing the way in which Frédéric Moreau loses all of his youthful ideals and becomes ever more jaded: with his security assured by an inheritance, his life becomes more and more aimless as he rejects or fails at each of the possibilities which present themselves to him. I like the way that money is written about so exactly in French novels of this period: as Frédéric's fortunes diminish, the amount he has to live on per year are given in precise amounts, and in all three novels money is dealt with very openly and precisely.
Le rouge et le noir also deals with a young man starting out in life, but a completely different man: Julien Sorel is driven and proud, a secret Bonapartist, the opposite of diffident Frédéric. This is a marvellously strange novel: partly a sort of satire of Romantic novels of young men setting out in the world - in Le rouge et le noir everything is so measured and calculated, every step Julien takes is because he feels he can move up the social ladder in some way - partly a cold denunciation of the France of 1830, with its hypocritical municipal officials, small-mindedness and the rule of the Catholic Church. Stendhal looks so coldly upon his characters and their motives for everything, but can't help every so often making a sly, amused remark about their behaviour which stands oddly with what feels like his disgust with the state of the world. 
Doris Lessing has written that "the ideal lover of Stendhal comes, as he did, from a family of conventional people in a provincial town... which is snug, complacent and reactionary, both politically and socially". In her Martha Quest novels, she describes the society she comes from: the white colonial world of Rhodesia. I read, or rather re-read, Martha Quest in the spring, and have now got round to the next two books, A proper marriage and A ripple from the storm. These are fantastic evocations of the time and place: the colonies in a period when liberation of the native populations was not viewed as a possibility, but also when the coming of the second world war gave the impression that everything had to change, and radically. A proper marriage is about Martha's stifling marriage to a conventional man and contains one of the most eye-wateringly horrific descriptions of institutionalised childbirth I have ever read, as well as evoking the bizarre provincialism and claustrophobia of the white world in Rhodesia in a very clever and dark way. In A ripple in the storm Martha has left her husband and become involved with a nascent, tiny Communist group, and bizarrely Lessing manages to make a book which consists of a series of political meetings very funny - as well as bitter.