The problem with an original assignment (which in this case I got from a book) is that its demands and effects become evident only after, sometimes, the writing is done. Some around the reading of it, not unconnected to the grading.
Students find this unfair, if grading standards are retrospective rather than prior in application, which I have to watch out for (or as Don Cherry would say, to the college grad hockey player at training camp who said "Coach Cherry, you can't end a sentence with a perposition": "Ok, 'which I have to watch out for' you asshole").
Students enjoyed writing the voice of a coach instructing and inspiring his/her players at half-time (but does Cranium have half-times?).
Trouble is, they wrote the voice and didn't speak it.