Almost Obsessive Attention to Form and Meter
Like many poets of the 1700s (Alexander Pope, we're looking at you), Thomas Gray was pretty obsessed with the form of the poem. You'll have a hard time finding a place where he breaks out of his rigid iambic pentameter or ABAB rhyme scheme. In fact, the Romantic-era poets (William Wordsworth, S.T. Coleridge, and others) were partly reacting against this kind of poetic strictness when they started writing in a looser, more free-form style in the early 1800s.