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