http://www.hardcoregaming101.net/kings-quest-iv-the-perils-of-rosella/
http://www.hardcoregaming101.net/kings-quest-v-absence-makes-the-heart-go-yonder/
http://www.hardcoregaming101.net/kings-quest-vi-heir-today-gone-tomorrow/
King's Quest IV - VI! IV is the first "evolution" that used the then-revolutionary SCI system, with higher resolution graphics and mouse control; V is another step up to the revised SCI system that added VGA graphics and eliminated the text parser completely; and VI isn't quite the same technical leap but is also easily the best written, most well designed of the series.