The thing about glasto is you can ditch all the main stage stuff if you want to - there's amazing finds on Park, Acoustic, John Peel, Other Stag, at the King's Head and randomly dotted around the festival.
I discovered Los Campesinos!, We Are Scientists, Elvow, Sons and Daughters, MGMT, CSS, Battles, Tunng, Emmy the Great, British Sea Power, Blood Red Shoes, Metric, Fucked Up, First Aid Kit & loads more - all at Glasto, so there's tons to discover.
That's probably what I love most about it - there's so many acts on that it's really a make-your-own festival