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.
Yes, well, that's kind of a given.
My problem isn't that fans are angry, it's that fans get off believing they (we) have a say in any of the above. That we should expect the writers and creators to write for our benefit. They don't and I don't think that that's a bad thing.