Is it just unreadable?

There is no denying that Hegel and Heidegger are difficult and demanding reading, but not insurmountable. What usually happens is that the reader feels absolutely lost until they finish, and then it all suddenly becomes clear.
Luckily, there are also commentaries that help the reader as he goes along by explaining important or obscure passages with reference to the whole, or restating the text in another way. In the case of Hegel and especially Heidegger, reading one or two commentaries before tackling the originals makes understanding the work much easier.
It also helps to read some of their "lesser" writings before starting to read the major opus. Heidegger's What is Metaphysics? or Hegel's Lectures on History for example, are useful introductions both to the general drift of their philosophising as well as their method.