Other than a pretty lackluster performance, I think Ghost doesn't work because of poor planning (or, again, last minute changes).
For example, I was playing the Daily Heroic Story yesterday, which had me on Mars fighting the Cabal. At one point, Ghost/Dinklage exclaims (in a pretty frenzied tone): "I'm getting a massive energy surge and it's NOT Cabal! Keep pushing on!"
Nothing wrong with that, except:
-It's a reference to the Vex, I guess? Which have already appeared in the mission, so they're not a surprise. In fact, it makes this line confusing.
-It's spoken during a lull in the action. So you're not really pushing anything, you're just walking through the mission.