These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: This film sharply divided M. Night's fanbase; some viewed the twist as terrible and invalidating the whole film, others thinking it worked and the movie was well-constructed, and a third camp who somewhat disliked the twist but appreciate the rest of the film. This division was the beginning of the decline for M. Night.
Ensemble Darkhorse: Say what you will about the story, but Ivy was a cool character and Bryce Dallas Howard knocked it out of the park performance-wise.
Idiot Plot: It's difficult to believe Walker and the town doctor couldn't foresee the utility of modern medicine in the Village's comparatively risky environment, and account for these needs. We're meant to believe this was a calculated risk, but after The Reveal of Those We Don't Speak Of, the same people should have considered a comparatively simpler disguised tunnel exit.
It Was His Sled: The titular village is not an 1800s town but secretly set in the modern day. Those We Do Speak Of are people in costume intended to keep up the masquerade.
They Wasted a Perfectly Good Plot: The film's twist ending renders most of the suspense completely pointless, since it completely removes the supernatural elements. Arguably, it would have been far more interesting had Those We Don't Speak Of become real as a result of the Villagers belief, which would have been more in tone with the rest of the film. Imagine the Oh, Crap moment if it instead ended with all of them slowly walking out of the forest, furious that the Villager's had broken the Truce?
The Film's original ending is this too. Imagine the implications of finding out that you live in a completely different time. That your parents have been lying to you for years. That deaths could have been easily prevented. How would you fit into a civilization hundreds of years more advanced with technology you never could have imagined? All of these are interesting premises that never get addressed.
Another good way to incorporate the twist is that both the village and Those We Do Not Speak Of are still real, and it's just that the people are still living like it's the 1800s because they've been isolated from the rest of the world since that time.
Alternately, Those We Do Not Speak Of get revealed and replaced by outside criminals, who'd love to have such a sanctuary.