I think they tried to lead into 12's dark side and jadedness with the name of the doctor and day of the doctor but 12 almost seems a complete departure. It makes you question how he could have even been any of those others with that attitude. I am not partial to Time Lord snarkiness lol What makes the Doctor such a fabulous character is that despite all he has seen and been a part of, he retains that child-like Peter Pan spirit. I think that is why we are drawn to him. We like to believe that we retain that as well.
Ahem, not that I've given it much thought or am taking it more seriously than a grown person should take something like this ;-)