Ezra Pound was a Modernist poet. The poem "In a Station of the Metro" is considered to be an Imagist poem. An Imagist poem, brought to the forefront of poetics in the 1920's, was poetry which depicted precise imagery and clear language.
The poem "In a Station of the Metro" is the quintessential Imagist poem. The poem depicts the honesty of precise words and nothing more. The poem, itself, is a sort of snapshot. Written recalling a brief moment in time, the poem describes a picture of a Paris metro during the 1920's.
Therefore, the poem, when looked at from the point of its form (Imagist), is not missing anything at all. The meaning of the poem is simplistic: a picture of life, a snapshot, a moment of time captured in poetic form.
One must understand how Pound wrote and what he meant to depict in his poetry. The poem is simple and concise, as was the moment in time Pound is detailing.