I finished reading Child of God this week, and... Wow. Still thinking about it.
I'm not sure how it compares with Outer Dark in the grotesque factor. I'd say for Child of God, the content matter was more disturbing in a.... grounded way. The descriptions left me feeling physically repulsed, as if I were reading an account of a crime that actually happened. The time period could have something to do with it, but it was definitely a lot easier to distance myself from the cruelties portrayed in Outer Dark (and Blood Meridian, for sure), despite how graphic they are as well.
From what I remember, Outer Dark also had a more fantastical (biblical?) element to it, almost reading like a twisted parable. And the mystery behind the "villain" figure definitely leaves it open to interpretation, whereas the themes in Child of God felt more straightforward.
Both are soul crushing and phenomenally written and left me feeling hopeless on the state of humanity (would not be a McCarthy novel otherwise, I suppose โบ๏ธ).
I am tempted to revisit Outer Dark now bc I thought I noticed a few similarities in McCarthy's word choices (which would make sense, given he wrote the two back to back). It might be interesting to document them here, like I did with some of my reading notes with C&P. We'll see.