I read the criticisms and did my best to go into the story with an open mind. Unfortunately, the critics were correct. As earnest as JKR's intentions were, she and her colleagues produced a thematically overwrought and too on the nose work.
It read like alt-timeline greatest hits fanfic with a frankly unforgivable soap twist. Voldemort would not have impregnated Bellatrix for any reason. He didn't think he would lose, so he wouldn't have required posterity to avenge him. Delphi would serve no tactical purpose in his eyes, and Voldemort wasn't capable of emotional attachments. Furthermore, Bellatrix as much as told Narcissa she would only use any children she had as canon fodder for Voldemort, and any Death Eater foster parents would have made that clear to Delphi. No any way you look at it, the plot point makes no sense.
I did love how they incorporated Snape. But, we'll sadly never see that bit in the inevitable movie, which I'll rent only for the returning actors.