The reading itself was, obviously, slow, and required a lot of back tracking. However, I found that if I put the book down for a while and went back and re-read part of it later on, that I'd discover some small piece I didn't even know was there. The text is so densely packed that it's difficult to just sail through it. I actually timed myself the first time I started reading it and found my pace at about roughly 10 pages per hour, which is, to say the least slow.
As far as my experience went, I've only read a select few books that made me feel the way this one did. I read through it over the course of two days, and by the time I was done, I felt genuinely...well, I felt pretty dark. I had the images of the dying slaves lying in the woods and decaying severed heads on sticks stuck in my head, as they were so vividly described by Conrad.
I loved the book overall and think Conrad had a lot to say that's still valid today. If I've interpreted it correctly, I think that I agree with a lot of Conrad's ideas about the artificiality and "lies" of modern civilization. Though he seems dire and cynical, I think there's a lot of truth there. I'll delve deeper into some of these issues on the other pages.