The most welcome surprises on the 2015 Lollapalooza performance lineup
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The 2015 Lollapalooza lineup is the strongest in years, thanks mainly to a willingness to move beyond the same tired artists who play every other major music festival. This time around, Lolla is bringing in some fresh faces atop its lineup along with a solid group of mid-card superstars (Alabama Shakes, FKA Twigs, Gary Clark, Jr.)

Which acts on the lineup are the most pleasant surprises? Here are seven that we're excited about.

Paul McCartney

Sir Paul always seemed like one of those artists who was “too big” for Lolla, especially since in recent years the festival chose to book retread headliners like Eminem and Kings of Leon instead of branching out to find new names. Thankfully, the former Beatle has signed on for the 2015 edition and will headline on Friday, July 31. McCartney's live concerts are legendary, and now that he's recorded with Rihanna and Kanye West, there's always the chance either of those superstars could show up for an unannounced cameo.

Charli XCX

Even though Lollapalooza doesn't book a ton of pop divas, the event always manages to include a couple of up-and-coming stars worth checking out. Last year Betty Who fit the bill, and this year it's Charli XCX, who appeared on hits by Iggy Azalea and Icona Pop before earning her own smash, “Boom Clap.” We're especially excited to see her perform her latest hit “Doing It” on the Lolla stage.

Of Monsters and Men

Icelandic rockers Of Monsters and Men were given a surprisingly high billing as the third act listed for Sunday, beneath only Florence & the Machine and Bassnectar. The group broke through with the adorable pop song “Little Talks” back in 2012, which was followed quickly by “Dirty Paws” and “Mountain Sound.” Of Monsters and Men just released “Crystals,” a track from their upcoming album Beneath the Skin, which is planned for a summer release, perfect timing for their Lolla appearance.

Metallica

The presence of the metal gods on the lineup was unexpected since they've never played Lollapalooza since it became a three-day festival, though they did headline back when it was a touring event in 1996. Metallica also haven't released a new album since 2008, but that won't stop James, Lars, Kirk and Robert from dishing out what is likely to be one of the heaviest sets in the festival's history.

Flying Lotus

Flying Lotus made one of 2014's best albums with You're Dead!, an impossible-to-categorize record that featured elements of hip-hop, R&B, EDM, jazz, and other genres that were mashed into an acclaimed album featuring guest appearances by Kendrick Lamar and Snoop Dogg. The chance to see how the Flying Lotus sound translates to the live stage will be one of the highlights of Lollapalooza this year.

A$AP Rocky

Hip-hop isn't huge on the Lolla lineup this year, but A$AP Rocky is the big name among a group that includes Tyler the Creator, Kid Cudi and Travis Scott. Rocky achieved success with the collaborative single “F---in' Problems” and “Wild for the Night.” The Grammy nominee and former boyfriend of Iggy Azalea hit No. 1 with his last album, Long. Live. ASAP.

Sturgill Simpson

Alt-folk always seemed like the domain of Bonnaroo, but Lolla jumps into the mix this year with the addition of Sturgill Simpson, whose acclaimed Metamodern Sounds in Country Music earned a Grammy nomination this year. It's always great when left-of-center acts appear on the bill, giving fans other options beyond just the famous hitmakers.

Lollapalooza takes place in Chicago's Grant Park from July 31 through August 2.