I never had a problem with the 'Nooooooooooooo' moment.
The critiscism of that moment seems predicated on the fact that it weakens the Darth Vader character, and that the character would never have showed such emotion.
But I would argue that at that precise moment, we were not looking at Darth Vader, but the last vestiges of humanity of Annikin Skywalker, not yet quite come to terms with his situation, his loss of humanity, his disfigurement, the loss of his wife, and indeed the end of his previous existence, and the realisation that he would have to spend the rest of his life encased in walking life-support machine.