The actor who learned he was playing Red John found out at the last moment. "He was thrilled," Heller said.

source: http://www.orlandosentinel.com/entertainment/blogs/tv-guy/os-mentalist-can-show-survive-without-red-...

All the other actors are too "seasoned" to be excited. :P
Jack Plotnick might still be pretty "thrilled" with this opportunity.