It depends on what you mean by attacking the creator - I know people who think that suggesting the writing wasn't perfect is an attack, or that mentioning/refering back to other things written by the creator in a review in a less than positive light is an attack.

Yes there should be things that are off limits for a critique, they include things like the writer's private life or mental state.

Anything relating to structure, plot, pacing, continuity storyline and it's relation to other published fictional work by the same writer is all fair game in my opinion.

And if the conclusion is that the writer produces great beginings to their stories, but is usually awful at providing a sensible endings, or that their writing style is formulaic, or that they use surprise endings so much that nobody is surprised by that fact that it is a surprise ending any more, then so be it. These are not attacks on the writer.