Easily my favorite take on the limitation, the soft game over where you can still move around is a super unique take, very clever!
As for the game itself it's just as amazing. Gameplay is very well made and enjoyable to play. The art is the strongest point, I really like the life indicator up top that changes expression as your health goes down.
Looking through the comments I see your idea on the horror elements and I think you should go for it, it sounds cool! Updating the game with those ideas would make it a really unique take on wave survival.