Drama; Realism; Tragedy
Drama
The novel presents small and large conflicts on both a personal and societal scale. This isn't the type of book we would read for its surprising plot twists and turns (though there are a few); instead this is more the kind of book that we read to get insight into human emotions and relationships. There are plenty of those to go around here.
Consider the scenes between Carrie and Drouet, Carrie and Hurstwood, or Hurstwood and Mrs. Hurstwood. These scenes are so long, and not just because we're given long stretches of dialogue—nope, we're also made privy to every last sigh, sniffle, or eyelash batting that takes place. We're given all of the nonverbal interaction that plays a huge role in human interaction, though that stuff could really be cut without losing the main thread of the story. However, it's included because that's the stuff of drama. And Sister Carrie has more drama than Facebook.
Realism
Sister Carrie is often deemed part of the nineteenth-century Realist tradition in literature, which is a lot like what it sounds like: literature that purports to offer a slice of life of ordinary people (instead of, say, kings and queens). We get to watch characters making awkward small talk about the weather and bickering over how much meat to buy at the grocery store.
We even get to see Carrie use a machine to punch holes in leather. Again and again. It doesn't get much more boring (er, real) than that. In instances like this, Dreiser's particular flavor of realism (sometimes referred to as Social Realism) exposes the problems of ordinary people, particularly the problems of the working classes and the poor.
Along that line, Sister Carrie is also sometimes considered part of an offshoot of Realism called Naturalism (a little confusing, but the more varieties of Realism the merrier, right?). Naturalism is often described as a grittier form of realism, so in naturalist novels, we really get to see characters' dirt. Like, literally. A good example of this in Sister Carrie would be when we're shown Hurstwood washing his face in the horse trough toward the end of the novel.
Yeah, we're definitely not in the land of kings and queens.
Tragedy
Sure, Carrie becomes a big star at the end, but she's certainly not happy. We might even say that she suffers a spiritual death. And don't forget Hurstwood—his is the classic tragic ending, with physical death.