Blake and Wordsworth, in spite of being approximate contemporaries, have relatively little in common as poets, in my view.
Blake is one of the most idiosyncratic and isolated figures in literature. His technique and his ideas often come across as having more similarities with the modernist poetry of the twentieth century than with that of his own era. The unexpectedness of his imagery, the unusual moral stances he appears to take, and the impression he sometimes gives of hovering on the brink of psychosis all differentiate him from Wordsworth and the other Romantics.
Blake obviously wished to express a "philosophy," though he did so in an unsystematic way—one that is both anti-religious and spiritual. He seems to believe in the vitality or the special truth inherent in opposites, in contradictions within the human psyche that incorporate the traditional concepts of both "good" and "evil." His intention is often to shock by upending our usual ways of thinking about social realities and the moral underpinnings of society. Few writers or thinkers have said,
Pity would be no more
If we did not make somebody poor,
And mercy no more would be
If all were as happy as we.
and yet at the same time:
A robin redbreast in a cage,
Puts all heaven in a rage.
Blake's poetry is disturbingly mystical. He reaches beyond the human world in cryptic statements that are both spiritually oriented and yet set up man himself as a kind of divinity. In saying the following, he draws from scriptural concepts but, as Nietzsche would later do, creates his own self-oriented religion. What else could the following mean other than that Blake sees himself (or the archetype of the poet or artist) as one in direct contact with God, or even as a god?
Hear the voice of the Bard!
Who present, past, and future sees,
Whose ears have heard
The holy World
That walked among the ancient trees.
Wordsworth, though his chief intention was to express the "spontaneous overflow of powerful feeling," was nevertheless more grounded to the earth and to ordinary human concerns than Blake. Wordsworth was obsessed with chronicling his own inner thoughts, the transcript of his mind, as opposed to putting forth a philosophy or expressing universal spiritual truths. He was constantly looking backward, examining how the past and his lost youth is recreated and transformed by the individual—meaning himself.
Blake is emotional to a similar degree, but the emotions that animate him are different from those that inspired Wordsworth. The latter, despite his greatness and originality, is a more generic and conventional poet than Blake.
The one thing that unequivocally links the two is that both use realistic language in their verse. Their poetry avoids exalted and unnatural "poetic diction," and both poets use the language of real people. With the exception of meter and rhyme, Blake and Wordsworth write the way people actually talk. This, more than anything else, sets them apart from their contemporaries.