The Whisperer in Darkness (2011) is a movie made by Lovecraft fans for Lovecraft fans. The care put into every aspect of the movie is evident throughout, making for a movie that even those not into Lovecraft will appreciate.
As it is with the Lovecraftian genre as a whole, In the Mouth of Madness (1994) won't be for everyone, but when John Carpenter is steering the ship, it's always going to be a fun ride!
J.K. Simmons voices a Lovecraftian deity speaking to a man through a rest stop glory hole. The premise is unique, but there's too little depth and this one runs out of steam pretty quickly.
An interesting premise, effectively creepy direction, and solid acting all become lost in a muddled, uneven narrative that fails to follow its own established rules.