Well, it's certainly basic. Nothing above and beyond my expectations. I do have a few small gripes with it, though. First, never... NEVER should the player need a key to access another key. For this reason, the first level puzzle is completely superfluous. Technically speaking, you can bypass it entirely and lose nothing in the long run. (I know I did when I got frustrated by knowing the puzzle solution but not knowing how or where to input it.)
Second, you wanna know how to break the game? Dash horizontally through a door... yeah, that's all. More often than not, a glitch will occur where your position is displaced on the map. You'll appear to move over one screen, but it will put you back into the room you just came from. And if you try to move up or down a floor after the fact, well... more often than not, you'll end up getting yourself stuck in the wall of the "secret" room on Level 2 (the staircase going from floor 2 to 3 is on the left-hand wall, and there's no door on that side in that particular room). Because of this, it's easy to ruin any save file because climbing any set of stairs automatically saves your game. In other words, you're hard-locked and any progress you made can be thrown out.
Third, and somehow this is the most annoying factor to me, is the Ghost Amulet. I expected my character to flicker or go temporarily transparent while invincible, but without keeping a keen eye on the icon in the top right, I have no idea how much longer my invincibility period lasts.
All in all... it was okay. The whole QR code aspect of the puzzle solving was just stupid, both because it essentially allows you to cheat and because there's no easy way to read a QR code from a Flash game... and even then, the hints were vague. It could've been worse, but it left a lot to be desired.