I only know Rory Cochrane from his role as Tim Speedle on CSI: Miami. That's pretty much the only show he was starring in according to his 'appearance' list. And his acting out this role wasn't really good, by the way.
He always had this pissed-off attitude about him. I don't know whether this was Tim Speedle's personality or Rory Cochranes. Either way, this made him totally unlikeable. Whenever he was talking to a (supposedly) suspect, spectator, or witness he had this kind of I-dont-care-what-you-think-cause-Im-a-CSI look on his face.
The summit of his annoyance was the episode 'Wannabe' in Season 2:
He interrogated this little (btw harmless) wannabe CSI. Throughout the whole time he talked to the guy in a condescending manner. Then, the next day they had to show up in court. In the elevator Horation told Speedle that the little geek wouldn't be coming. To which Speedle excruciatingly annoying replied: "Why? Does he want us to pick him up?" But it turned out that he was found dead. At the end of the episode, however, Speedle was portrayed as the only one who ever believed in the little geek and that he had a special relationship with him. What in the world???
All in all, I think Rory Cochrane is heavily overrated. I have to admit that I'm glad that the writers decided to kill his character off and replace him with Ryan Wolfe, who is way cooler, IMO.