The amount of wordplay and poetry in the writing gives a certain feel to the text. Wordy, writerly, ornate, extravagant, flowery text must only fill a certain percent of the novel. Purple prose by any other name would overfill a tweet. If verse crowds out the plot or characters, the readers may be found lying dead, smothered on their couches, book draped over their face. A purple shroud. On the other hand, if the prose lacks poetry, you may be better off reading a newspaper to tally puns in the titles.
The words create a sense of atmosphere which is critical to the story's universe (or at least to preserve life on the planet). An honorable knight can only exist in the two dimensional space of parchment, scrawled over with epic poetry. Cthulu can only breathe in Lovecraft's dripping, overwrought, and anxious prose. No matter what world your fiction is placed in, your tone needs to match it and supplement the story. This applies especially if it is fantastical or sci-fi; you need to find a tone that will aid and abet the suspension of disbelief.
Twilight and every other supernatural romance is changing the tone for the supernatural from the unnatural to the pedestrian romance. But hey, it sparkles. There must still be some magic! A farce, but in a sense it works; the twilit tone is one of denial. Denial that vampires are a bloodthirsty lot. Denial that the relationship is inherently and utterly deranged. Please, dear supernatural romance writers, kick it up a notch. I think it is high time that this genre takes its psychopathology out into the open.