At least according to one review, from 1984, in Electronic Games Magazine:
Don't be fooled by the unimaginative title. King's Quest is a major breakthrough in action-adventure games. The quest itself is clean-cut and simple-an excellent primer for a novice adventurer-but it's combination of keyboard-input and joystick operated on-screen character movement blows everything away.....(goes into a summation of the game elements)....
Agan, as a pure adventure, it would hardly be worth a second glance. But in simplifying the puzzle-solving and Zork-like elements, and instead, overwhelming the player with lush graphics and joystick control over the hero, the vistas of adventure gaming suddenly open to a whole new audience.
Hmm...Good for novice adventurers, simplified the puzzle solving elements, opened up the adventure genre to a wider audience...sounds familiar.
Then we come to KQ5, which did away with keyboard interaction completely and dumbed down the game play even further, with a very simple point and click interface. Sierra did this once more to open the series up to a larger audience, and expand the genre beyond it's core audience--to make it more accessible. Then came KQ6, which placed story telling on par in importance with the puzzles...Then KQ7 came, which got rid of the narrator and reduced the level of interactivity and softened the puzzles, again, to open the series up to a larger audience and make it more accessible....Hmm.