There's so much going on in this short novel / story. The horror of European pillaging in Africa. The petty concerns of selfish functionaries whose only talent, only virtue, only superpower is to stay physically healthy in a place that routinely kills other Europeans through indigenous people's attacks, through disease, and through technology break downs.
As you no doubt know, the movie Apocalypse Now is based on Heart of Darkness with some exact quotes but moved around. The phrase "for my sins" is much later in the book, and the movie uses it differently, for example.
But the questions of Truth and of moral responsibilities are posed in both the book and the movie. It's a short enough read, so give it a go and see what you think.
In these times where persons of color are writing their own view and voice of some Western Civ stories and tropes, I wonder how someone of that culture(-al) background might re-tell a similar story?