King's Quest 1 was the first game that impressed me deeply and made me notice videogames as a medium and format with vast potential to go infinitely beyond the arcades of its time, in which you just played an eternal repetition trying to reach a good score. Not that I am against this kind of game, hell I still play a lot of stuff like that to this day, but we couldn't just stop there and KQ's contribution was paramount for this.
The feeling of adventure and fantasy that the series provides - especially 1, 3, 5 and 6, and yeah I played them all - is unparalleled, and Roberta Williams' huge sensibility to transpose the magic feel of fables and folk tales to the games is definitely something to be noticed. Somehow makes you see things with children's eyes again, with that mixture of curiosity, excitement and awe.
Small note on the compatibility topic: simply apply the patch that can be found on Sierra's help page (you can easily find it around here, the community hub and the forums) and they all work perfectly.