I truly think that what makes the sucess of a character is the right balance between how the character was orignally written, the choice of the performer and how he/she decides to play his/her character, often up to bring some personal features after several seasons, when the actor/actress definitively feels more confortable with his/her character.
For ex, to perform someone like Kathryn Janeway, it was necessary to have a natural presence and authority, what Kate Mulgrew had without a doubt, from the
intonation of the voice to the posture. Geneviève Bujold*, as a fine actress she is (and she trully is talented!), was unable to exude (naturally) any form of authority and presence, which was much needed And to be totally convinced, just listen what actors like Wang and McNeil, Russ who shooted 1 or 2 scenes with Bujold and Mulgrew, used to say.
*Bujold was 52 yo when she began to shoot for Voyager while Mulgrew was 40 yo. And then, usually, Starfleet's captains have a strong personality, are physically active. Can you decently imagine, Bujold as Janeway, in actions scenes? Or flirting with her XO, what was Taylor's idea? In both cases,I'd say "no".
