First of all, maybe the issue its not the square models, but the texture.
Tiling
https://gyazo.com/74f77687236fe67c70c33c0d7eee1814
Texture blending
https://gyazo.com/3fffea6afb45f56c88e1186473d89f95
and over all the character model, and some other models on the map had the fuzzy texture
https://gyazo.com/247e633af07644eb0c8a14b357f8095f
something like this
https://gyazo.com/43fc35de35df4d8bbbbc113df7b9033d
but in dark fantasy style (btw ToonCar is a good reference for models shape imo, but maybe your should looks a bit more spooky)
But these square walls uses more realistic style brick texture, which seems like from the another style game.
https://gyazo.com/217a61ccc2998c9690a9a4e769ad941
and this seems off.
About the boss. I feel like there should be an attack, that is quite hard to dodge, so it will serve as a time limit. Noone will want to let the boss use this ability too often, so everyone will try to speed up the boss when he is easy. Speeding up things makes the mistakes.
Also, it will be more fun if there will be a possibility to deal more damage by doing something. For example hitting weak spots, or a heavy attack but with long recoil, or a poise bar on the boss.
And its only my opinion. Over all good job!