I watched "In the Mouth of Madness". It's honestly weird that it took me this long, because I generally like Carpenter's films a lot.
I mostly knew what the movie was about, and had known some of the specific plot. So the movie was about what I expected. No shocks and only some surprises, sadly.
That being said, it's still a great movie, which I thoroughly enjoyed. It's probably the best Lovecraftian movie that's not an adaptation of an actual story by Lovecraft. And possibly the best Lovecraftian movie ever, period.
Pretty much everything about the movie worked for me. Sam Neill is cast perfectly as the main character, the story is both a bit mind-bendy and makes perfect internal sense, I liked the special effects, the acting, the visuals (especially the lighting), the weirdness... everything. It's just a damn good movie. Critics must've really hated Carpenter, between this movie and the "The Thing" being disliked by them. I honestly don't get that. "In the Mouth of Madness" is perhaps not the perfect movie and maybe not for everyone, but as far as I'm concerned, it's the perfect version of what it's trying to be. It's a horror story that's smart while not putting on airs of importance, which kinda reminds me of Stephen King - the other clear inspiration for the script besides Lovecraft.
Also - stories that include heavy metafiction elements can be tiresome, but in this case, I didn't mind. The movie is not cliché as far as I'm concerned. It's more creepy than scary overall, but it works really well for me.
I do wish I'd gone into it completely blind, but even knowing some of the plot points in advance I didn't feel like my enjoyment was ruined or anything.