I’ve done it with a few Sierra games. It’s not that hard if you’re familiar with the game. Most difficult thing is not falling off narrow paths. But it all depends on the game. Games like the original King’s Quest were difficult because of the random baddies that run out and kill you. The random nature of the games requires some luck. So it’s impressive winning King’s Quest II without saving since it had a few of those. I think I did it for Space Quest 1-2, Police Quest 1, and maybe King’s Quest III. I don’t remember. Those were the games I played the most.
