The question pretty much answers itself, but in case you're wondering if seeing Styx, Foreigner, and Def Leppard together in one venue on one night might equal the concert-going experience of your lifetime, I can confirm: hell yes it does.
Okay, so it's kind of like a live, much more expensive version of the jukebox in your favorite bar, but after Styx played "Renegade" during their encore, my roommate was so, so right when she said, "That alone was worth the cost of the ticket," and I dare anyone else on that sold-out lawn to disagree. And yes, Foreigner is basically a cover band anymore, what with only the original guitarist still around, but when the former lead singer of Hurricane (na na na na na na, I'm on to you) does his best Lou Gramm impression in really tight pants through a set of every Foreigner classic you could think of requesting, you don't really care, even if you're an unironic Foreigner fan who's seen them in concert with the old lineup intact.
We weren't that interested in Def Leppard—who were headlining—going into it, but they played a long, rocking greatest hits list, and both their guitar players are disconcertingly buff and topless, and they've got a bass player whose every not-so-dramatic costume change came with a new correspondingly coordinated single fingerless glove. (I love you, Rick "Sav" Savage!) The above elements plus beer plus yelling the words to "Pour Some Sugar on Me" along with several thousand middle-aged white women and beefy dudes in sleeveless T-shirts pretty much equals the best Tuesday night ever.
Unless you happen to live near one of the four remaining tour stops, you probably won't get to experience a slice of this three-tiered rock cake yourself. At least this year. The bands tour pretty regularly, and if the onstage antics of their spry front men (picture lots of senseless running to and fro) are any indication, they'll be up to it again soon. If you're lucky.