"Proper adaption" is a very narky thing to say.
There has already been, by definition, a proper adaption of the original Pokemon games. Liberties were taken to expand the world sure, but that was mainly to fill in the story gaps and embellish the between-gym route journeys that, let's face it, were less than spectacular in the original Game Boy iterations. Compared to Fire Red and Leaf Green, the originals were quite terrible and succeeded mainly on hype and media tie-ins.
Some people are sick of Ash being the main hero of the story in current seasons. That doesn't make the original anime any less relevant to the franchise. It's like saying the original Dracula novel by Bram Stoker is not a real interpretation of vampires because everyone's sick of them being in movies like Twilight today.
But I digress. This has been confirmed as a one-off special, not a new series. It looks really nice and I'll watch it and probably love it, especially since it looks very close to Ken Sugimori's art from the manuals.