What is the effect of Fitzgerald's use of these loose/cumulative sentences in The Great Gatsby?We walked through a high hallway into a bright...

I've been rereading your question about the passage you quote from The Great Gatsby for the last 24 hours, trying to figure out the answer for you.  I'm not at all sure I've figured it out, but since no one has answered it yet, I decided to take a try at it. 

I think the sentences leading up to the final sentence create a soothing effect.  The images are presented in long, slow sentences that create the effect of a lull.  This mirrors Nick's pause as he listens.  The sentences seem to roll, like the sea that is mentioned, perhaps.  Contrast these sentences with short, simple sentences.  I cannot imagine the same effect being created here by short sentences.

The effect of the sentence structure changes in the last sentence, however.  To reinforce the "boom" of Tom's closing the window, the writer must destroy the illusion quickly, abruptly.  He manages this by compacting numerous details into the one sentence, the most important of which are the falling of the curtains, the rugs, and the two women.  The lull is over.  The more compact the destruction of the illusion, the more abrupt it seems, and the more Tom is revealed as the novel's destroyer of illusions.