I found the text is hard to read. The white outline is a little too close to the grey, making the words blurry. The text on the character select cards is also fairly small, and I had a very hard time reading it until I zoomed in on my web browser.
It would be nice if I could have navigated the title page and menus using only the keyboard. I think it was most noticeable on the Character Select screen, where I could use either keyboard or mouse to switch between characters, but couldn't use the keyboard to select ready or how to play.
On the Carpenter's description, "Though he works with wood, he has always had an affinity for wood" sounds odd. Starting with "though" makes it sound like the first part of the sentence is at odds with the second. If he has an affinity for wood, saying something like "He works with wood, which he has always had an affinity for" would get your point across better. Of course, if he has an affinity for something else (which I'm guess is the case since your magic is fire, earth, and heal), then the "though" would be just fine, but the "affinity for wood" should change to whichever affinity he has.
I didn't see any way to pause or exit back to the menu. Since you have multiple characters to choose from, having an easy way to return to menu and start a new game with a new character without beating the boss or refreshing the page would have been nice. Even something like giving the option to continue or return to menu if you die would have been nice.
Collecting items felt clunky. It was really easy to push items away from me as I tried to pick them up. I'm pretty sure I lost a couple of apples that way, and I lost my first chance to get fire because it rolled into the water.
It would have been helpful if you mentioned in game that you need to press E near the yellow blocks to lower bridges. It's not clear in game what you are suppose to do with it.
I started by using the Guard, as it was the recommended class for single player. The spell slots were a little unclear to me. I started with the apple and had revive greyed out. One of the items I picked up was a revive, which added color to that spell slot. The next one I picked up was fire. My final spell slot would alter between stone and heal, based on whichever I picked up last. I'm not sure if the load out was because of which character I picked or because of the order I collected things. It would have been nice if I could have picked what think I swapped out. Apples didn't really feel useful once I got Heal, since they both healed me for the same number of hearts and Heal was unlimited.
Rereading the itch page, I noticed that you could click and hold a number to drop an item/spell. That wasn't mentioned in the game itself and wasn't particularly intuitive to me to do on my own.
I started a second run with the Carpenter. An enemy dropped a fire spell before I got to any other spells. It went into slot 1, and when I picked up the fire spell that was sitting out, it went into slot 2. I picked up a revive and used it right away. I died after using it, but it didn't revive my character. Looking at the directions again, I think to use it on yourself, you are suppose to just pick it up and it will auto use if you die, but that is not very clear and doesn't match anything else in the game. I'm not as good with slower characters, and didn't really feel starting over from the beginning again. That said, I think Carpenter could be fun for someone who enjoys playing slower, hard hitting characters.
I didn't try the other two characters or the multiplayer mode. They both felt like they would have been much harder to use single player, but I think they could work well as part of a multiplayer party.
I didn't have issues with the controls, though I have played other games that use WASD and JKL. I might have changed Interact to J, though it felt just fine using E. Changing what ability you could use and casting/using an ability felt fine to me as well. It did sometimes feel like there was a little lag in using spells, though that might have been the fact that I was trying to use something too quickly after attacking.
I think the art is working, though there are a few things I think could be improved. All four of the characters had the same basic clothes and colors, and I think it would have been nice if each character had a different base color. That said, I didn't play on multiplayer, so if you are using different colors for that it would make sense. The characters all look very similar and would be hard to tell apart on a glance if they colors all stay the same. Giving them each a different hair style and/or color would also be a nice touch. The Yellow Blocks felt a little out of place, and had a placeholder feel to them. Making them look more like a button, switch, or lever would help make it clearer to the player what they are for. I like the enemy art. They looked good, both alone and with the rest of the art.