Style is something that is both obvious and hard to define. My sense is that there have been several different ways of dealing with it.
One is to compare how the texts of the NT and compare them with contemporary standards of rhetorical style. I'm thinking of the work Hans Dieter Betz has done for Galatians.
Another is to go computer and have computers do the style analysis, generally for authorship discrimination. David Mealand has been doing work on this recently.
Yet another is to give pragmatic or discourse explanations to features that used to be called stylistic.
Personally, I think that all three approaches have their merits.
Stephen C. Carlson, Ph.D. (Duke, New Testament)