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Jesse Spencer, Chicago Fire
Previous Greatness: He starred on House for eight seasons as perhaps the most loyal diagnostician on House's team.
Although it's nice to see Spencer shed his lab coat and get his hands dirty as Lt. Matthew Casey, there's no getting past it: Spencer struggles with masking his native Australian accent in nearly every scene of this generic NBC procedural. You'd think that with the constant threat of death-by-fire and Casey's somewhat compelling dual estrangement from his wife and best friend, we wouldn't notice the accent so much. But we do, and it's distracting.