I only recently found out that an original version of Blake's The Tyger is in the Fitzwilliam Museum, Cambridge - metres from where I work. It's one of the most anthologised poems. If you've only read The Tyger you might be surprised to learn that Blake's often considered a difficult poet. During his lifetime he had admirers but he also had detractors. When he died in 1827, the detractors won, and he fell into neglect for decades. Gilchrists' "Life of William Blake" published in 1863 gained admiration for Blake first from the Pre-Raphaelites then the wider reading community, but his mass-appeal was procured only by ignoring his later work, taking the pictures away from his early poems, and isolating his poems from each other. What remains is the Blake that most of us know.
When students study Blake in more depth, they discover that he intended the pictures and poems to be seen together. The pictures add new meanings to the words, and don't always support them. Moreover, when the poems from Songs of Innocence and Experience are read together, connections appear which undermine the apparent simplicity of the poems. Blake had many interests (the plight of exploited children in London, etc) that are there in the pictures, and once you see them in the pictures you begin to see them in the words. In his later work Blake invented a complex Mythology whose Gods were partly from existing Religions and partly based on his friends and enemies. Critics said that
Nowadays many of those earlier adverse reactions still persist. In the "The Cambridge Companion to William Blake" by Morris Eaves, it's suggested that students are offered 3 ways to cope with the difficulty of understanding Blake
I have a feeling that some writers today sympathise with Blake, especially those who are trying to combine pictures with words, or are resisting the lures of popularity. They'll face the same accusations that Blake faced. Blake's work is hard to analyse if you break it down into bits before trying to get a feel for the work as a whole. Northrop Frye (an important US literary critic) wrote that Blake "gives us so good an introduction to the nature and structure of poetic thought that, if one has any interest in the subject at all, one can hardly avoid exploiting him".