I think you nailed the tense atmosphere of early-game King's Field. And you start the game on a beach too, yeah...? I'm still not entirely convinced about that description, though.
Actual spoilers (I'm trying to make the text as small as possible)
I got the chills when the hidden stat appeared and the classmate mentioned feeling powerful after eating the red flowers.
You absolutely nailed that moment. The first dialog with the "surely dreams can't be dangerous hehe" also really stood out to me. It ended up being a very good horror/adventure experience for me. I got ending B first, since I couldn't resist.
And that Shadowman on the bridge made me shit my pants and fall down to the onis below. Which is a good first encounter, as it made my future encounters with them more tense (until I started farming them for Spider Lilies and lost all respect). Out of all your jam games, this is probably my 2nd favorite, and by far the most mechanically accessible. I'd play a full game like this.
And a bug report:
One of the walls in the first corridor with enemies, just before the mirror room, actually isn't solid. It's to the left when entering from the turn after the tutorial signs. Player's looking for a way to get behind the mirror (like me) are likely to fall off the map here and lose a few days of progress.
Really, you ought to implement something that kills or respawns the player if they fall out-of-bounds. I think I've managed to enter the void in all of your games that I've played. Just add a simple check on the player's z-coordinate already. It's like 2 lines of code.