Maybe Coleman discusses this, but Shatner's biggest problem isn't that he's bad, it's that he's often a lazy actor. He's admitted it himself in recent decades, he just saw Trek as a gig to make some money, and often didn't make the same effort with the scripts the other members of the cast did, especially Nimoy.
Many years ago some Internet forum or other held an informal contest where you had to hypothetically pick four items in a store that would cause the worst reaction at the checkout. The one that always stuck with me was: a bag of charcoal, a package of skewers, a jar of BBQ sauce, and a rat-trap.
Evidently the original look for the Klingons was created on the fly by actor John Calicos and a Star Trek makeup artist as the first Klingon episode was being prepped, because no one in authority had bothered to describe their appearance.
One classic Far Side strip has a scientist coming to a bad end when he uses his time machine to take a large rectal thermometer back to the Age of Dinosaurs to conduct some tests...
Reminds me of the original Star Trek episode where an Earth ship visiting a distant planet left behind a book about the Chicago Mobs of the 20's, and when the Enterprise arrived years later, the natives had modeled their entire society on it.