Though we've seen them interact -- as enemies and allies -- many times, it's safe to say that Cornell and Woods' "Lex Luthor vs. The Joker" will make quite an entertaining read.
Cornell has a better handle on Lex Luthor than almost anyone I can think of in recent memory. The calculation... The arrogance... The utter disregard for human life... Cornell (ably assisted by Pete Woods) give me a Lex Luthor that is as perverse and twisted and evil as any character ever. And yet... I can't look away. Because he's also as fascinating as any character ever.
Paul Cornell has proved that he can write villains. In addition to Luthor we've seen Gorilla Grodd, Vandal Savage, and a host of others. But what will happen when Lex Luthor meets his "polar opposite?" The Joker can't be reasoned with. He can't be intimidated. He can't be bought. None of Lex Luthor's usual tricks will work.
So what happens when Lex Luthor meets the Joker?
This is going to be a contest for the ages.