To be honest True Detective s1 didn't cast FoTM actors. Harrelson is known as being a psycho on set, and he was cast right after Rampart psychodrama. McConaughey was in a better shape, he went from shitty romcoms to "that guy" getting solid pieces in under the radar movies (tho he was decent in both U571 / Frailty and that film with dragons).
I'm excited about Farrell / Vaughn cast. They're both competent actors and they did either nice and terrible stuff. Everyone remembers Farrell as Alexander in Oliver Stone movie. On the other hand he did a nice job in both Miami Vice / In Bruges. It's kinda refreshing seeing this kind of casting, rather than having "True Detective season 2 starring Chris Pratt, Jennifer Lawrence and Robert Downey Jr as the villain".