One of the best actors in LOST. He play the role of a genius physician very well. Even though, scientific subjects in lost are extremely "crazy" with travel in time and such... He succeed to talk about these things in a manner that make them a little bit "acceptable". I mean here the manner of acting and not the content it self.
Definitely a nice and "necessary" actor. Imagine Lost without a genius scientist that try to explain things a little bit. Personally, I think that even his appearance and voice are very adequate for his role. Great actor and one of the bests!