Of the Apocalypse Trilogy, In the Mouth of Madness is the only one I didn't like upon first viewing. I didn't "get" it, but I sure loved the soundtrack, enough to special order it from Karma Records in the late 90's.

I didn't watch it again until I was well into adulthood and had developed a near-pathological enjoyment for Lovecraftian horror. Once I realized it was cosmic horror, I 'got' the picture, and it's been part of my collection ever since. Such a great, enjoyable, ahead-of-its-time picture! :)