Have you considered changing the title to "3 hp to wipe them all?" Haha, just kidding!
I honestly really liked the gameplay, despite not being very good at it (only once reached wave 4). Stuff like the delay before the (very wide) attacks start, the enemy types, the shield and reduced movement, it all ties together well IMO. I did use the shield, it worked against the large enemies of wave 2 which would kill me if I tried to sword them.
Gameplay wise I only have one thing to say: you seem to be heading down the path of "Struggling with wave 5? Have fun doing the first four waves over and over again just to get another shot at it". If you are going to make the player die in 1 hit, then death should not be too punishing IMO: you should either not loose a lot of progress OR it should be easy not to die. Or you could just not care about it and filter the casuals, it is your choice how noob-friendly you want it to be.
As for ideas about stuff to add... I feel like there are a lot of possibilities. Area damage spells, paralyzing/slowing down spells, spells that repel one type of enemies but not another, temporary barrier spells (to cover your back), a pet dog. Different weapons. Or how about this: a spell to transform into a dragon! Ok, I think that's enough ideaguing for today.
Anyway, looking forward to seeing this next demodays!