To a certain extent, my comments are highly stylized; that's not to say that they are repeated student to student, but rather that I definitely still use many of the techniques that I learned through the Knight Institute at Cornell, which definitely has a very prescribed program of how student writing should be commented-upon and marked. But it works, so I stick with it. Examples of the techniques include: descriptive rather than prescriptive commenting and sticking to the text both to model good analysis and to avoid passions running high when papers are returned (ie, "The essay lacks specific citations" rather than "You didn't cite your sources").
But this most recent assignment for my intro lecture course offered students a choice of three essay prompts, one of which tended more towards creative writing: Students had read a work of short fiction in which a Christian count laments his flagging popularity and his adviser recounts to him the story of an Umayyad caliph who expanded the Great Mosque of Cordoba, making that his legacy; I asked the students who chose that option to write their own short work of fiction in the same style, reflecting some aspect of the ways in which Christians and Muslims viewed each other's cultural achievements. But now that I have the assignments in hand I'm not really sure how to write comments on these effectively. If anyone out there has experience in marking and commenting on more creative-type writing (I hate the term, because it implies, especially to students who may not really know any better, that a really good analysis isn't creative, but that's beside the point) in a literature/history class, I'd very much appreciate hearing how that worked out.
Edited on 4/2/12 to add an image of the assignment sheet to facilitate the discussion happening in the comments thread:
(Click to enlarge to readable size.)