Of course, this list should really include the works of Marx. But The Communist Manifesto doesn’t have much to do with what I thought Marx was, or what anyone else thought Marx was afterwards. It’s just a piece of old-fashioned politics. And Das Kapital is one those books that people claim to have read, but no one has really read it to the end. Still, it accumulated into a creed.
One has got to remember that some of the people who were strongly influenced by Hegel are also not that easy to read. Kierkegaard and Schelling studied Hegel closely and neither of them is particularly easy to read. Marx worked on parts of Hegel’s Logic which then went into his doctoral dissertation and into DasKapital, which isn’t an easy read. Heidegger read parts of Hegel, Gadamer did, Derrida did, Hyppolite did. None of these people are easy.
I chose The Communist Manifesto, rather than, say, Capital because it shows in a much easier-to-read, shorter work something that is central to Marx’s vision. Capital is much drier, and a lot of it is focused on economics, although there are some remarkable passages of Capital describing the conditions of industrial workers in England at the time.