Because it's so often misunderstood, I've decided to stop teaching Heart of Darkness. Some of my students just aren't capable of detecting the irony that is one of the most important features of the text. For a text that more obviously attacks Europe's disgusting conduct in the Belgian Congo at the turn of the century, I recommend Mark Twain's satire "King Leopold's Soliloquy."
It's fine to criticize Conrad for marginalizing or excluding women, but that criticism needs to be grounded in the facts of the text for sure. Given how disgusting and depraved the world of the novella is, one might be relieved to be at the margins of the text rather than at the center. Feminist critiques are more effective with texts that purport to address women's issues. It's also worth noting that the representations of men and masculinity in the text are far from flattering.