Satisfactorily authentic. Except for the focus on Duncan Idaho from the beginning, this felt more like a prequel to Dune than a prequel to all six Dune novels, which was fine for me because I remember Dune a lot better than the books that followed.
While the writers were playing in Frank Herbert’s sandbox, they are playing almost entirely with his toys without bringing many new toys of their own, so this lacks the outflow of rich invention that is part of what makes Dune such a mind blowing experience. This is not the case with the story, though. There aren’t many new inventions, but the story is intriguing and compelling.
I guess you could say Frank Herbert invented the car and drove it well. Brian Herbert and Kevin J. Anderson don’t put anything new under the hood, but they do drive it really well.
Finally, I liked the way that the writers put little summaries of the story inside the story. For some people this may be repetitive or seem like dumbing it down, but for me it was welcome. I didn’t have too much trouble following the Dune books when I read them as a younger man, but I am now a lot busier, and appreciate these little moments where something like, “Leto considered the events that had brought him here. He wondered why X had happened, and when that had led to Y, he regretted having to do Z which had led him inexorably to this point.” Sure, it feels a little contrived, but these guideposts let me get right back into the story after a hard week and I appreciate it.