Well, this is a book that demands your full attention. No comfy reading on the couch while you're husband is watching a movie with this one! The story jumps around in both character perspective and time, without even indicating this by a using a paragraph break. Nowadays, we're spoiled by chapter captions telling you the exact date and - especially in crime/detective novel - occassionaly even time of day described, but Conrad considered his readers were able to find that out for themselves. Or he was just being a very true early modernist.
Besides the swifts in time and people, the plot is complex in itself. It's done brilliantly though, and actually it's amazing how Conrad manages to create a fictional country with a rich and complex political history, including a society and a whole lot of key characters with their own personal history in *just* 600 pages.
It's a story that shows how the idea of money and wealth destroys even the most sober and noble-hearted people. It's a story about colonialism, about Europeans treating indigineous people as savages (something that Conrad is guilty of himself, according to Chinua Achebe) and them trying to force their political systems onto worlds and societies that are incomparable to theirs. It learns us that money and not individuals actually rules the world and that greed makes people as unreasonable as can be.
It's a tough read, but this book definitely is a great literary accomplishment.