Blake was very much influenced by Milton, who as you mention is most famous for his unrhymed iambic pentameter epic. Blake used this `blank verse' rarely. His long words, of which there are several (the several minor prophecies, The Four Zoas, Milton, and Jerusalem) are mostly unrhymed, but include rhymed fragments and some very beautiful `traditional' poetry. There is a song in the preface to Milton beginning, `Did Not Those Feet...,' which Edward Elgar set to music during the Great War, and King George V said he would prefer as the national anthem over God Save the King. But by and large the epics are in kind of dry and actually often subtly sarcastic verse whose rhythm mostly derives from counting accented syllables per line. Except for The Four Zoas, Blake illustrated all of the epics by hand through engraving techniques he pioneered himself; then he would paint the individual books with watercolours.