The Slum is not hard to follow, but it asks for patience: the plot is clear, and what wears the reader out are the long chapters, the large number of characters and the language of 1890.
What helps is the plot, which moves in a straight line: a shopkeeper gets rich, raises a tenement, envies his neighbor and ends up returning an enslaved woman to captivity. The characters are fixed in a single trait, and the scenes stay in memory: the morning of the tenement, the pagode, the razor slash, the fire. Chapter I already introduces João Romão, Bertoleza and the tenement.
What weighs is its length: about 81 thousand words in 23 chapters, from some 1.2 thousand words in chapter XVII to some 6.7 thousand in chapter X. There are many people on stage, beyond the fourteen characters the book follows most closely, and the vocabulary is of its time, with terms such as cavouqueiro and jiraus. The naturalist descriptions run long, as in the morning of chapter III, with "a scorching heat" that "bit at their heads, blazing and glistening with sweat", and there are scenes of harsh violence, illness and downfall.
A reader who wants to go in with less effort can read the book through the three threads that run through it: João Romão's rise, the life of the tenement as an organism, and Jerônimo's change. The chapter-by-chapter summary, in another question, helps you find your way.