Express Scripts does value their employees and, in my experience, for the most part treats them right. Management is not above the law, and there is a very good culture of listening to employees and honestly trying to get the job done as best as possible. They used to have a reputation for working their salaried employees to death, but they have over the past ten years taken some major steps to address that.
Cons
Still worried about policy changes post-acquisition by Cigna. While I am unaware of any recent major layoffs or other cost-cutting measures, I fear they are coming.