Jane Jensen's epic masterpiece is nothing else than one of the greatest adventures ever - I would even go as far and call it one of the greatest games.
The hand-painted background graphics are still beautiful today (try using a filter like 2xSAI and choose VGA instead of VESA), the voice-acting is top notch and the music is hauntingly beautiful.
There are some hard puzzles but it never is illogical or even nonsensical if you examine your surroundings and talk to people. I finished GK1 in '93 (I think) without any help and the game never left my harddisk.
Like a good movie that you can watch over and over again, you can play GK1 again and again it's just that good.
And the best thing: There are two more GK-games. Get them!!