Pros
Excellent compensation, benefits, the unique environment, and the opportunity to try lots of things. You get to work with other really smart and motivated people. The software itself has some cool aspects and has been really innovative at times. It's nice to work for such a successful company.
Cons
After a while QA starts to feel more menial and less satisfying. It helps if you can switch things up or test in a variety modules. There are some flaws in Epic's development process that are really frustrating. Many of the developers you work with are mediocre at best. The most skilled developers tend to get recruited away. Periodically there are periods of high stress where you are pressured to work evenings weekends to try to fix some crisis that you may or may not have had anything to do with. This isn't so bad at first, but after a few years, this becomes really obnoxious. Many people leave for similar reasons, which makes it difficult to maintain relationships with colleagues. You don't want to get too attached to someone.