MM and MM2 were unique. I don't remember a lot about MM, except that there was a force field at the very end that I never could figure out how to cross.
MM2 was really, really different. for one thing, it had a castle that you could (with much effort) claim and fit out as your home, complete with trainers (for leveling up) and a merchant IIRC, before Bethesda ever came up with the idea for the same thing Elder Scrolls series. Gender played a role, too. There were certain areas that could only be accessed by females, so that first, you had to have at least one female in your party, and second, you had to leave the males waiting by the wayside while the girls went into the otherwise-forbidden area. Instead of buying spells, your mages/clerics had to run across them or receive them as loot. To cast, you had to type in the exact wording--difficult for not-so-dexterous players. Also IIRC, there were magical areas in the clouds you could sometimes teleport to.
All in all, groundbreaking in their own way.
P. S. I didn't care so much for King's Quests so much as Hero's Quest (true RPG, as opposed to adventure.) Sierra later had to change the name to Quest for Glory, because there was already a Hero's Quest out there (that nobody seems to remember.) I had both versions, and Quest for Glory is slightly different than Hero's Quest. I've still got the boxes and manuals, but the 5.25" disks somehow were destroyed/lost--who knows?