Naturalist
Okay, so Crane is a naturalist (more on this over in the "Genre" section), so it only makes sense that his writing shows many of the signs of a naturalist style. To this end, this book is filled with grim descriptions, dialogue steeped in dialect, and absolutely no sentimentality whatsoever. Look at these Irish immigrants in conversational action:
"An' wid all deh bringin' up she had, how could she?" moaningly she asked of her son. "Wid all deh talkin' wid her I did an' deh t'ings I tol' her to remember? When a girl is bringed up deh way I bringed up Maggie, how kin she go teh deh devil?" (13.4)
There's a real allegiance to detail that emerges here. Crane totally could've written: "And with the bringing up she had, how could she?" But he doesn't—he takes the time to try to capture the pronunciation and rhythms of Irish American speech during this time and area.
As for grim descriptions, even when Crane is describing somebody appealing, it's tinged with darkness. For instance, check out this bit from when Maggie first meets Pete:
His hair was curled down over his forehead in an oiled bang. His rather pugged nose seemed to revolt from contact with a bristling moustache of short, wire-like hairs. His blue double-breasted coat, edged with black braid, buttoned close to a red puff tie, and his patent-leather shoes looked like murder-fitted weapons. (5.10)
We totally get that she digs him—there's a lot of detail given here, indicating attention—but we also totally get that he's bad news. Just look at some of the words tucked in this moment of admiration: "revolt," "bristling," and "murder-fitted." Yikes, right? But that's the whole point: Naturalists aren't trying to give readers hope, so even when characters have hopeful moments, Crane makes sure we know not to hop on the bandwagon.