I guess that technically Mark is the main character - but I pretty much look at this as an ensemble show. I agree that Mark's character isn't strong so for me I'm more interested in Weddick, Demetri, Zoe, Janice, Olivia (when she isn't whining), Aaron (when he isn't whining), the young doctor at the hospital, and the Mysterious Persian woman (Nahda, I think).
I love the actress who plays Nhadra Udaya aka the Persian woman (Shohreh Aghdashloo). She is top notch! Oh well, you know this show is dying when I gotta respond to posts from 2009