Level of polish is amazing. Great and challenging game.

Lots of polish and lots of fun! love it

The game feels very polished, and great to play too, all of my suggestions have been commented by other people below, so I suggest you take a look at them and take them into consideration :)

Fun gameplay / overall idea, good use of assets. I think the souls shouldn't disappear after each round, though.

loved the gameplay, very addictive. And overall very polished game, congrats.

Great job with the visuals overal! And the gameplay, too. It was nice having to choose between upgrades or staying alive, gave the game a feel of depth. Maybe trying to lower the upgrade prices a bit would be nice

Excelent work on the lighting <3

It seems to me that you are a Dark Souls fan which is highly appreciated! Great job on the lighting,  the morphing which is really interesting and the hit effects,it feels impactful. Cheers!

An all round good game with some tasteful lighting, nice polished attacks and interesting choices between sacrificing souls for longevity or absorbing them for upgrades. To improve, I would suggest:

• Perhaps lower the prices of upgrades towards the start of the game - during the first few levels it is impossible to purchase anything. 
• Give the player some time between the end of the round and the upgrade screen to pick up souls, as during the wave it is hard to focus on collecting and attacking

Cool idea! If you want to keep it as frantic as it is right now it would help if you could tell which souls were what enemy. As the maps get harder it's harder to keep track of them all and if you're any of the slower units you're not collecting them as soon as they die, so you have to sort through a bunch at the end of the round.