I Think The Descent Into
insanity works best when your starting point isn't Nic Cage.
Stephen King expressed a similar thought regarding Kubrick's The Shining. King always envisaged a 'normal guy' eventually unraveling to the point of being crazy and murderous, but that effect is sprung a bit early when Jack shows up on screen. Then, it's more a waiting game than a surprise.
Plot Hole - the most overused and least understood phrase at IMDb