For such a large festival, Bonnaroo is great. It's admittedly been awhile since I've been back, but the atmosphere is made by just how great everyone is to each other. I'm not an outgoing person, but all the conversations with strangers with everyone so open and friendly is half of the draw for me.
You'll literally get some of the biggest names in music as headliners, but its lineup is large and diverse as hell every year. Unlike some other larger festivals, it kinda never stops either. There's music playing until sunup.