Amazing game!
The first thing that stands out is the art style. It looks so good! I love how it looks. I can't really describe the style or effects used but suits the theme sooo well. The mistery of having weird runes and trying to decipher them is a cool idea, I had a lot of fun doing so.
I like how the main door is always there at the start, but if you want to understand what any of it means, you have to go to the rune guide, which is the actual game in which you discover what everything does. Only then can you go back to the main door and open it when you finally understand it all.
The audio design it top notch too. The cave SFX like fire and water dripping sets the mood very well.
I have to admit that the first few times that I unlocked the door I did it by clicking the runes at random. It seems to be very easy to do so! I didn't even understand how any of it works but I still was able to open it, which obviously is something no to be desired. Any player will instinctively just click things at random so this could feasibly happen, but of course we want the player to go through the guide!
One of the things I would personally change is the arrow icon that you use to convey the meaning of "this on the left turns into this on the right". For quite some minutes my mathematics a** was thinking of the symbol "greater than" instead of just an arrow since they are the same. So I was a little bit confused by that. Maybe it's not that common for people to think that though.
One of the best so far <3