Mark Hamill happens to be a huge DC fan, and in an interview with Polygon it's noted Mark Hamill start reading DC comic books first. The articles says Mark Hamill loved the performance of Jared Leto as the Joker in Suicide Squad and added he hasn’t seen an interpretation of the Joker yet that’s made him go, "That was terrible." Hamill further says Jack Nicholson’s Joker in the 1989 Tim Burton Batman movie was very different from Heath Ledger’s in Christopher Nolan's The Dark Knight "simply because it had to be."
"Everyone brings a different spin to the character and you have to look at each script separately," Hamill offered. "I don’t think there’s a definitive version of the Joker, and I don’t think there can be. It’s like Hamlet, really. It’ll be constantly redefined."
It's further reported that Mark Hamill says he can sympathize with people who are upset over the direction of the DCEU, but Hamill wouldn't specifically comment on Man of Steel, Batman Vs. Superman or Suicide Squad.
Mark Hamill did point out that if one man was in charge of the entire production, then the group of fans who are displeased with what they’re seeing on screen aren’t going to be able to necessarily do anything about it right now -- a reference seemingly to Zack Snyder who directed two of the previous aforementioned movies, produced Suicide Squad, is producing the upcoming Wonder Woman and is directing Justice League.
Mark Hamill did share some advice for fans in that they should never stop letting their opinions be known because it "absolutely makes a difference for future films."
And speaking of the Joker, it appears as if Mark Hamill might be offering up his own version of the Clown Prince Of Crime this season on The Flash.