The twists aren’t so twisty, overly telegraphed to the point of being easy to see. However, the movie stays afloat above its necessity for subterfuge with careful direction and captivating atmosphere.
A house/hospital full of stuck people, literally and figuratively, makes a strong setting.
It is funny that you can walk away from the movie thinking Poirot gives some credence to mysticism or that you think he gives zero and everything can be explained. It makes for a little extra engagement.
I have a real soft spot for these movies. Even flawed, Hercule Poirot and Branagh are an attractive pair.