I'm not going to go through a detailed outline of all of the interview, because most of the reviews do a pretty decent job of that. However, one thing I did not find prior to my interview was enough relevant information on the presentation in my opinion.
The presentation is very informal. They tell you that you can use any topic and they are not kidding. I chose a relatively serious, business related topic for my interview, and I almost felt out of place. Every other candidate I spoke to presented on things such as how to throw a baseball, their favorite sports teams, or where they grew up. I don't know if I stood out because of my business-like presentation, but my advice to you on any topic that you choose is to be knowledgeable. They will ask you questions that are intended to make you think on your feet. Just make sure you know what you will be talking about, and you will be fine.
Epic does not allow use of a PowerPoint, however, prior to giving the presentation, they allow you to use a whiteboard to write or draw anything you see fit. Use it. I think this is an underutilized asset, especially for business-related presentations. You will seldom be in a meeting where visuals are not utilized in the presentation, so show them that you can use diagrams and/or bullets to make your points. This should go without saying, but make sure whatever you write or draw is a useful asset when presenting. Don't draw a fancy diagram just because it looks fancy.
Again, know your topic. I cannot emphasize this enough. Know your topic. The presentation should not be a point of stress in your interview, but if you don't know your topic and stumble choppily through it, it will become one.
All in all, the interview process at Epic is a great experience. You get the ability to network with all of the Epic employees you meet as well as the other recruits, and that is invaluable. Make use of the opportunity. The food is great as well. The tour is phenomenal, and it's great to see the different parts of Epic's campus. It looks like a very interesting and exciting place to work, and I look forward to confirming this shortly.
Good luck!