The headliners are weird. Maiden and Metallica are fairly standard and predictable but The Prodigy
Are they even rock/metal?
The Prodigy have headlined Download before. Not a band i would choose to see but as i've got my ticket for Sonisphere I'll watch them.
As Sonisphere was cancelled two years ago and didn't happen last year they needed to guaranteed "bums on seats" headliners to re-launch the festival in the UK, hence Maiden and Metallica.
Maiden have said they will be doing a re-worked "Maiden England" set, but including more of their rarely played, these days, early catalogue. Metallica's set is "by request", so their set list will be chosen by the fans.
For me Alice In Chains, Mastodon, and Airbourne are great additions to the line-up!