We'll get to that in a minute. First, let's get the obvious out of the way: sometimes Lawrence really sounds like a goon. For example, he tells us, via the narrator, that Clifford "really reaped the fruits of the sensual satisfaction she got out of Michaelis' male passivity erect inside her" (3.98). If this sentence doesn't make you cringe, you've got a stronger constitution that we do.
Is it purposeful? Is he trying to point out that Connie's relationship with Michaelis is a little gross? Or does he just need a better editor?
Most of the writing, however, is in a grand style that we're going to call "vatic" but could also be called "prophetic" or, if you were feeling cranky, "pompous." A lot of it takes the form of a repetitive circular style that's characteristic of modernism.
It looks like this:
What's going on here is that, near the beginning of the book, the narrator says, concisely, that Clifford's sister "had departed." That's it. No information about that sister—who she is, what she does, why she left. Just, "departed." In the next chapter, though, the narrator returns to the same word—departed—but builds on it to give more of the story—she left because she was unhappy that Clifford married.
The narrator uses this technique over and over. Here are two more examples:
Time went on. Whatever happened, nothing happened, because she was so beautifully out of contact. She and Clifford lived in their ideas and his books. She entertained...there were always people in the house. Time went on as the clock does, half past eight instead of half past seven.(2.40)
In this passage, the narrator starts with the short phrase "Time went on," moves forward to describe Connie's life, and then returns to the phrase and expands it, like opening up an Easter egg to find something more inside: "Time went on as the clock does, half past eight instead of half past seven."
And then later:
Round the near horizon went the haze, opalescent with frost and smoke, and on the top lay the small blue sky; so that it was like being inside an enclosure, always inside. Life always a dream or a frenzy, inside an enclosure. (5.2)
Here the narrator fixates on the phrase "inside an enclosure," playing with its implications and meanings. The prose is circular and repetitive, but it always adds more information the second time, expanding and building as it returns to the original almost like going back to the scene of the crime.
Considering that lots of scholars think of "trauma" as the fundamental condition of modernity, it makes sense that the narrator would keep coming back to the same language as though processing traumatic stress.