Pros
There are a lot of good, hard-working, down-to-earth people here. If you can find yourself in the right position on the right team, you'll have opportunities to work on a diverse set of projects in a fast-paced challenging environment with smart people. PTO is pretty good.
Cons
If you find yourself on the wrong team, you'll be managing tedious second-rate processes with limited impact and no real hope of making a significant difference. If you enjoy treading water you'll be fine, but if you get bored of the same thing every day you may not be happy. There are jobs like this at every company, but the size and growth of Express Scripts has made these positions much more prevalent than they used to be. It's much more likely to find yourself in one of these dead-end positions nowadays. It feels more crowded than it used to, and the roles are smaller and more focused on mind-bending levels of detail about really specific things. Actually getting meaningful things done has become very difficult as it requires weigh-in from countless people with their own highly specific needs. Decisions only get made at the VP level, and then often with politics and turf fallout. If you find yourself in a losing or forgotten piece of the organization, jump ship - trust me, you'll be sorry if you don't.