Well he can most certainly write a badass Lex Luthor that's for sure.His Batman vs Luthor arc in Batman confidential was fantastic.
It's good to know that he wrote a good Luthor story. I'm looking forward to seeing more of Lex in the New 52 as it is. However, it has been easier in the Modern Age for writers to connect with Luthor than with Superman. Paul Cornell had better reviews when his Action Comics featured Lex while Brian Azzarello's Lex Luthor: Man of Steel was received a whole lot better than his run on Superman. Diggle is a great writer but he reminds me more of Azzarello than Morrison. That's my concern.