I remember reading Moby Dick a few years back and feeling the same way. I’m glad I read it, but it wasn’t easy.
As sort of a pre-psychological exploration of “madness,” Kurtz and Marlowe are interesting portraits of someone gone mad with power, and someone obsessed with someone mad with power. It’s also a very damning portrait (unintentional on Conrad’s part, I think) of colonialism. Chinua Achebe long ago labeled Conrad a racist, and rightly so.
There are two other things I found difficult about reading it. One is that Conrad gives no one else besides Kurtz and Marlowe names, a stylistic choice, no doubt, emphasizing that neither character values anything about the world beyond their own obsessions. The other European characters get labels (ie. the manager, the Russian) and the natives are described in barely animalistic terms (hence the racism charge). While I could see Conrad’s reason for this choice, I found it difficult to engage with the novel as a reader. The effect of all these vaguely described characters kept everything at too much of a distance for my liking.
The other barrier for me is that Conrad just tends to prattle on. Hemingway would have captured a ten page Conrad scene in two sentences.
Still, I’m glad to have read it, and I’m looking forward to seeing Apocalypse Now again soon.