The problems he addresses still abound and it's really a pity we have culturally suppressed the vocabulary and arguments he put forward to talk about them.
So, my guess: serious.
It doesn't get into politics the way a typical work on political theory might, but that is, I think, very much intentional. Capital centers on the problems and politics of its day, while attempting to critique and respond to them. It does this by establishing a thorough foundation for a better politics focused on achieving a very particular goal--obtaining true freedom from [social/political/economic] coercion and domination. That it seems ahead of its time is a testament to it continuing to be relevant--because the issues it focuses on continue to exist.
That Capital is so widely misunderstood--both by those who turned it into a foundation for totalitarian negation of its foundational principles, as well as those who hold that regrettable history up as an indictment of the principles themselves--is regrettable, and the world is worse off for it.
If you're interested in disabusing yourself of the notion that Capital is an analysis of automated manufacturing, and not a proper work of political theory, I'd wholeheartedly recommend the exceedingly approachable and well-cited book Marx's Inferno by William Clare Roberts. Roberts, in my opinion, gets Capital (and Marx) right--and presents an incredibly compelling argument for a literary connection that really is a first of its kind. Then I'd recommend re-reading Capital, while reminding yourself that Capital is on a mission, and that mission isn't to explain how manufacturing works. :)
It struck me that my favorite intellects usually do foremost concern themselves with “how poorly we understand systems and why it's critical we get better at managing them”. This intellect just seems most important right now.