He’s a classically-trained Shakespearean actor, trained with the Royal Shakespeare Company. You should check him out on his The Twilight Zone episodes. They’re about the hammiest, scene-chewiest things you can imagine. 
While he was a Shakespearean actor at Stratford in Canada, and in fact was Christopher Plummer’s understudy before taking on leading roles himself, Shatner’s US career kicked off in the 1950s in film noir. He was considered a quite serious actor.
Didn’t he prefer theatrical acting & live audience and thus played his TV role like a theater actor would? I vaguely remember reading about it.
Those tend to traditionally exaggerate gesture, mimic and tone so the last row still gets everything even when they’re further away.
He’s a classically-trained Shakespearean actor, trained with the Royal Shakespeare Company. You should check him out on his The Twilight Zone episodes. They’re about the hammiest, scene-chewiest things you can imagine. 
What, food? Naw, this cast eats the scenery. But there’s a grill in the back alley if you wanna cook something.
While he was a Shakespearean actor at Stratford in Canada, and in fact was Christopher Plummer’s understudy before taking on leading roles himself, Shatner’s US career kicked off in the 1950s in film noir. He was considered a quite serious actor.