The original King's Quest games set the framework for what every adventure game that came afterwards would follow. For that, they deserve a lot of respect, even if they are flawed games. While they are charming, the difficulty level is quite ridiculous! You can die instantly and unexpectedly, and can end up in a situation where late in the game you need to restart because there is something you didn't realise you had to do earlier on. It's important to save your game VERY often.
Completing these games without using a walkthrough is an impressive task, and I tip my hat to anybody who has managed it. I personally own a fantastic book called 'The King's Quest Companion' which contains walkthroughs for each game presented as novelisations, and is a fantastic read.
From a narrative point of view, the first two games aren't particularly noteworthy and reference a lot of fairytales. The third game, however, presents a story much more intricate and interesting. It's also worth taking note of that fact that these games really pushed the envelope in terms of technology for the time when they were released.
These original games are certainly worth experiencing for their place in games history, as without them many of my favourite games would probably have never been created. I would, however, recommend also playing the fan remakes that exist for these 3 games, as they are of a professional quality and add a lot to the gameplay experience.