If you don't read Das Kapital, you don't understand Marxism but are instead gleaning it from other sources that only partially cover it, generally for the purposes of their own applications. A lot of people do just go with Lenin or Mao and then constantly fuck up because they do not in fact live in conditions where there's a substantial peasantry or a monarchy. Once they realize this, they don't know what to do - how to "update" Marxism, as well as how to criticize it. IMO this is also why Trots and Gonzalites and so on can proliferate so easily. I have yet to see a Trot reading list that includes Das Kapital, but they all call themselves Marxists. A large number that I've interacted with don't even know the basics.

It's also not very dense, it's just tragically German. Once you get used to the writing style and maybe a little Hegel it's a fairly quick read. The real barrier, to the extent that there is one, is just to set aside reading time at all.