Pros
Epic's culture encourages ownership and the huge customer base gives developers many opportunities to have a big impact on healthcare. Because the company is privately held and led by developers, decisions are made for the long-term instead of for a quarterly stock market valuation. Executive leadership has the will to make hard decisions and stick with them. Developers have a lot of independence on design and implementation of projects. I've never been given a spec to go code - I've always just been given a problem and asked to solve it or a high level workflow idea to investigate. Almost all developers do full stack, and you're involved with the full life cycle of projects. You'll talk to customers, write the designs, create the UI mockups (with UXD help), implement the design, and help users during go-live or at post-live visits. You'll see your code in action while patients are receiving care. I've never been discouraged from pursuing a good idea I came up with myself. I might have other work I need to do (e.g. customer commitments, bug fixes, etc), but if I'm willing to put in the time to get the development done, we'll find a way to get it reviewed and released. These "extra time" projects are some of the things I'm most proud of. Product teams have gotten fairly large as Epic's grown, but individual scrum groups or functional area teams have stayed small so that you know the people you work with pretty well.
Cons
With quarterly releases the time from QA complete to in production for enhancements is much faster than it used to be, but I still wish the feedback loop was shorter. Healthcare providers are naturally risk-averse (for good reason), but I'd love to get to a place where we could get new features to production environments faster.