I agree, can't stand 'em, but festival headliners are usually the bands with the mass appeal.
I seem to remember Glastonbury got slaughtered a few years ago when Jay Z headlined... at least they were throwing something a bit more challenging up there. The best stuff at any festival, but probably more so Glastonbury than anywhere else, is on the smaller stages. I'm amazed people can be bothered slagging off the Stones. What were they expecting? A bunch of 70 year old blokes roll out the hits on the main stage and it's not blow your mind exciting. Was it ever going to be anything else?
Agree with those who've praised the Portishead and The xx sets. The Portishead live Roseland NYC album is amazing, well worth checking out.