All the Pretty Horses isn’t all that bleak. More of a western Bildungsroman.

Not really. Suttree is not exactly a happy story, but it has beautiful prose descriptions of filth and the Tennessee river, great rendering of vernacular language and culture, and some hilarious laugh out loud segments (the watermelon incident, for instance). It's probably the least dismal of his books, tone-wise.

They're all sort of heavy and with grim parts but I think the two you already read are the most disturbing by far. There are some parts of his other books as intense as those two but they aren't pervasive.

Suttree is semi-autobiographical.

There is less violence and more drinking than his other novels.

It doesn’t really investigate morality in the ways most of his novels do.

It is the last of his early novels set in Appalachia.