I think it's very valid for Gen Urobuchi (Urobuchi Gen?) to decide he has more to say on the themes and ideas, and the fact that it's been years since the last installment makes me more hopeful that it's the case with the new film. Yes the series stands on it's own as an individual work and I have no issue with people deciding to not watch any sequels because they don't think it needs them, but I'm willing to see where he's going here.