There certainly feels like there's a bit of lost potential here. The concept of characters meeting their shadow selves is interesting, and could be an excellent way for characters to confront their own flaws and self doubt.

However, this just... doesn't happen. Shadow Ace and Shadow Hex are largely apathetic and uninvolved in the story, not serving any meaningful narrative purpose.

On top of that, the whole plot thread about the native Umbrians being displaced and the rage of the planet itself seems tacked on, and isn't explored in enough depth for it to really pay off. It has potential, but it falls a bit flat.

The highlight of the episode for me was the Doctor doing a little dance with his shadow self to save the day. Was it tacky? Yes. Was it at odds with the tone of the rest of the story? Sure! But McCoy does silly like an expert, and it was a delightfully clownish sequence that made me laugh. Sometimes, that's enough!