Love it! You made it really interesting and fun to play with the combat. I wanted to keep playing and even lost myself in it at one point! I think you did a great job crafting the experience!
I do have some feedback, though!
My biggest complaint is QOL! Please, let me walk by holding down the key; that is psychological warfare! lol
It's an easy thing to overlook, but oh man, some of the levels were big, and I was so annoyed being forced to tap the keys every time I moved :D
The lack of a map or clear visual indicators/breadcrumbs to tell where I was and where I needed to go was another big QOL improvement I would have liked to have seen. It didn't help that from a distance, the wall textures obscured the doors.
Also, it would be really nice to have some kind of mouse-over indicator or something for the area of effect on the spells. It seems dumb, but it is really easy to misjudge if an enemy is inside them or not, especially when you are changing them often.
There are some obvious things that I think were just the result of time constraints as well things that most jam games suffer from. More audio variety, environment dressing, some more systems, and a bit more depth on existing systems would have been nice, etc. I think this game would work great with an exp/stat system, so you have the ability to invest in HP or mana and maybe allow enhancements to the spell tree in the long term just to provide more build variety and complexity. Also, damage types, enemy resistances, and effects are always a safe bet; I think they would all work well if you planned to continue working on the game.
Outstanding submission though, really enjoyed it!