Hearing this poem could be compared to a great Italian opera. Italian opera is known for being incredibly ornate, elaborate, and over-the-top (think of the Three Tenors, singers breaking glass, etc.), and that's just what this poem is. You'll be bombarded by a ten-dollar vocabulary word in almost every line: "apparitional," "panoramic," "derricks," "reprieve." Crane rarely uses the simplest word he can find: his powers of language are like a full orchestra, and darn it, he intends to use his players to the hilt.
Italian opera is highly Romantic, in the sense that it's less about logic than big ideas and emotions. Crane's poem is like that, too. He trades in Big Topics like freedom, modern urban life, and the potential for unifying the nation. The music of his poem is in the sound of its words and the power of its images. And with Crane this "music" is almost always soaring, sometimes literally, as with the gull in the opening "shedding white rings of tumult." White rings of tumult! It hardly gets more Romantic than that.
The poem moves very quickly, from image to image, metaphor to metaphor. There's not much time for the reader to process what's going on. The quick pace is due in part to the heavy use of enjambment: when one line spills over into the next without a pause. For example, Stanza 4 has three straight lines of enjambment (in other words, the phrases carries over a line break without a major pause):
And Thee, across the harbor, silver-paced
As though the sun took step of thee, yet left
Some motion ever unspent in thy stride,--
Implicitly thy freedom staying thee!
What on earth is going on in the lines? What is the sun doing? What is the bridge doing? Why would anyone in the 20th century still use the word "Thee"? Don't worry, it's just like Italian opera: few people go and see an opera by Verdi or Puccini and sit there with the lyrics, pouring over the meaning of each and every line. The words are really just a vessel for the beautiful music, and if you can catch the gist, that's good enough. Try to listen to this poem in the same way. Don't get caught up in the meaning of each image or line: just let the total experience wash over you. And if you really want the full, three-hour opera experience, try reading all of Crane's book-length poem, The Bridge… aloud!