I personally did not find this game fun (but only only because this is not my style of preferred game). However, I did find it very challenging and engrossing~ which in a way I could see why certain types of people would find this fun. The mechanics of this game are deeply involved. What starts out as seemingly complex, becomes simple if you stick with it and don't mind reading a lot of text. If you are a puzzle game player, this is most likely something you will really enjoy. While I don't mind a puzzle game, I would prefer not to have one with a lot of text, so this was just not my kind of game. it demands your attention to decipher text clues to solve puzzles. The text clues however they are generated, are a very clever way to have you think critically in order to decipher the puzzle. The text is very flavorful, especially if you like fantasy genre type settings or games. There is a lot of color association too which helps you to further reason and make connections.
To me, this is a game where I recommend you read the instructions very carefully because jumping and in just trying to figure out everything feels very overwhelming and complicated because it demands so much attention to the details that are within the text. But for you to associate and make the connections needed to play the game to its resolution, guessing would feel impossible (though it's not). I went through and read and was like okay.... now I see...
Given this is a very heavily text based, I would consider the readability of the text colors against the brown UI. It is very hard to read the Blue and Purple against the brown, and even some other colors clash. The White and the Black text are the easiest to read, Yellow for Light and Cyan for Wind are beneath that level of readability. Under that level is the Orange/Red for Fire and Green for Earth. Blue for Water and Purple for Dark seem to the most difficult to read. And if you are committed to the color, consider adding a black stroke to the text element, this may help a lot but keep the commitment to your color association.
The audio is very complimentary and even though there is 1 music track that loops, it doesn't get boring. It feels fitting for the genre and feels fair while thinking and solving the clues. The game is very static (which is not a bad thing). If you were to consider any additions, I would say some audio feedback for click events, maybe even hover sfx. UI animations would make the game feel more lively and interactable. Like when you have the runes selected, consider running particles or animations on those UI elements as they are selected. I personally think it would be neat to animate the fire in the background since your eyes are drawn to it and the blue fire color compliments that overall brown UI and main static game environment.
Overall this is a great project, a lot of thought went into weaving the aesthetics, genre, and theme. Great implementation of puzzle mechanics in a clever and unique way. If you enjoy using your brain for text puzzles, this is definitely a game to not sleep on! ;-]