I have to admit that this novel is one of my favourites, and I also love the way that F. Coppola did an updated version of it in his excellent film. Of course, the film focuses and comments upon the Vietnam war rather than colonialism in general, but I think there are definite parallels between the two texts.
One key difference between the texts is that Kurtz in the novel is a station manager working for the Company whose job is to get as much ivory as possible. Kurtz in the film, however, is an officer in the American Army whose job it was to subdue the natives and hold a station deep up-river.
Apart from this, there are mainly similarities: both are deeply charismatic figures who subdue the natives in part through their sheer charisma and rhetoric as well as through terror. Both are figures with incredible promise, but who have "gone bad" because of their isolation and the arena they find themselves in without any social checks on their behaviour. In the film, Kurtz is assassinated by Marlow, whereas in the book, Kurtz dies from an illness. However, both characters - the Kurtz in the film and the Kurtz in the book - act as a memorable warning of the corruptibility of mankind - even the most civilised example.