When analyzing a poem, it can be helpful to put what the poem contains in contrast to what one would reasonably expect to find. This is especially helpful with Blake, who seems highly self-aware of his poetic style and diction.
In English, the benchmark poetic line since at least the Renaissance has been iambic pentameter (five feet of breve/stress rhythm). This is what we see in Shakespeare's sonnets and blank verse and it is by far the most common poetic line in English. It is the natural rhythm of English speech, the natural beating of the human heart, the way we walk. It's just hard-wired into our sense of sound and rhythm.
In "Tyger," however, Blake gives us lines of trochaic feet (stress/breve), which are the opposite of iambic:
Tyger Tyger, burning bright,
In the forests of the night;
What immortal hand or eye,
Could frame thy fearful symmetry?
Generally, trochaic rhythm can be a little off-putting because it feels familiar but just a little wrong. Note that this is the same beat Poe uses...
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