"The Conqueror Worm" begins with an anonymous speaker introducing the poem's central extended metaphor:
Lo! 'tis a gala night
Within the lonesome latter years!
Beginning the poem with the word "Lo" (that is, "Behold!") creates a sense of heightened drama right off the bat. The speaker is commanding the reader's attention much as a narrator might at the beginning of a play. And life, this poem says, is nothing but a play—a horrible, ugly, nasty, pointless play.
Here at the beginning, though, the play feels rather glamorous. A "gala" is a special event where people get dressed up and enjoy live entertainment. That this particular gala is occurring in "the lonesome latter years" may feel a little mysterious at first, but basically the poem is suggesting that this poem takes place late in the history of humanity. The /l/ alliteration in these opening lines ("Lo," "lonesome latter") adds rhythm and intensity to the speaker's introduction. All told, these first two lines suggest that something grand and dramatic is about to happen.
The poem uses accentual meter, meaning that it doesn't stick to any consistent metrical foot (like the iamb or the trochee). Instead, it just uses a certain number of beats per line. Poe chooses a strange and unpredictable accentual meter here, veering between lines with three stresses and lines with four (though he'll sometimes dip down as low as two). Listen to the first two lines, for instance:
Lo! 'tis a gala night
Within the lonesome latter years!
These lines don't follow a standard pattern of feet, but they do use three beats, then four. The way in which Poe arranges those beats will change across the poem, keeping readers on their toes.
The poem also follows a strict ABABCBCB rhyme scheme. Across the eight lines of the first stanza, then, lines 2, 4, 6, and 8 all rhyme: "years," "tears," "fears," "spheres." This flamboyant, insistent pattern alerts readers that they're in for a wild ride!