I was invited to Epic's Campus for an interview about 2-3 weeks after their recruiter had visitied my University and I took some of their tests. (Programming, Math, and Logic). They flew me out to Madison/Verona for a couple days; 1 was spent exploring the city and surrounding area (my choice, self-lead), and the other was spent doing the all-day event that is the interview process. I was in a group of probably 50-75 other candidates being interviewed that day. Some of the day was spent seeing demos of their software, talking about what interns get to do during their time working, and having actual one-on-one interviews with other software developers. Dress code was as relaxed as I've heard. No suits, no ties. T-Shirt, cargo shorts, and sandals are perfectly acceptable. I was regularly offered snacks and refreshments which were readily available just about anywhere.
The best way I would describe the process is very warm and friendly. It didn't feel like an interview at all; like they were more focused on getting me to like them instead of vice-versa.