He's indeed very special and looks like he's writing to himself (especially in his last works). However, after trying to understand his last works for 3-4 years

He's indeed very special and looks like he's writing to himself (especially in his last works). However, after trying to understand his last works for 3-4 years in full-time, I can't say he's "crazy". I would rather say that he gave up trying to make his texts understandable, and he probably has fun writing like that. I once met him and he said jokingly that he was a poet.