In The Mouth Of Madness

The best thing this movie does is balance jumpscare/gory horror with psychological/atmospheric/surreal horror.

The worst thing this movie does is have an underwhelming ending that feels like a shrug or a bunt, instead of leaving us with true ambiguity or a memorable visual/scene. Though it's a cliche, I think a Mobius strip style ending would have better served the narrative.

Some would argue it's debatable if the events of the film happen at all, but I think that's not the intent, given that John Carpenter considers it part of his Apocalypse Trilogy. I believe the intent of the film is a double twist, that everything really *is* happening AND, ironically, the main character we've been following *isn't* real and is a creation of Sutter Cane. (I think that's why his character is an actor in the movie at the end, like how you see Bond movies billed as "James Bond in...Moonraker.") 

I think the revelation of Sam Neill's lead as a fictional character could've been done better rather than Sutter Cane just telling it to him face to face. Hell I'd even settle for something like he dismisses it in the moment but later it's revealed to be true. Maybe with him returning to his home and finding someone else living there or calling up an old friend who no longer knows him, something like that. Keep it ambiguous if the book publisher is still somehow doing a proto ARG to promote the book by fucking with his life like that.

Ultimately I think this is a film that approaches greatness, and has many great things going for it, but there's just a bit of a muddled and hollow/unsatisfying feeling to the whole thing by the time it's over. If you've seen other "is this really happening/what is reality?" films, even non-horror/scifi ones, a lot of the tropes and ideas here will be familiar to you, albeit they are well done tropes and not mere cliches lazily followed. It certainly helps that the cast is excellent, though holy shit Sam Neill's accent travels as much as he does in the movie.

In The Mouth Of Madness sets itself up to be a 5 star classic for most of its runtime and then limps to an ending that has no stakes. Why do I say that? Well, because it turns out the main characters never had any agency to change anything at any point: one of them isn't real so nothing he did ever really mattered, and Sutter Cane's writing makes everyone else behave as he orders them to. There's an unspoken consequence to decisions like this in movies, including the audience becoming uninvested in the narrative, and it certainly makes rewatches pointless because every action the characters take is preordained and not due to who they are and who they become through the trials and tribulations of the plot. Though this movie is mostly excellent, there's a nagging asterisk that needs to be placed next to that excellent to qualify it.