I think we have to be cautious about forming too rigid a view of any actor in his first appearance in any role. It takes a lot of them a little time to get to grips with the character and indeed writers may not always have decided where they're going with that character.
Good point. If you watch the very first CSI episode, they haven't quite got Grissom's character down yet. He occasionally throws a "punk" up against a wall and mouths pretty standard TV-cop dialogue. The bemused eccentricity was something they developed more later.
And I think I remember reading an interview with Nimoy where he talks about finally getting a handle on Spock.