Solid game! I like how heroes always stand in a formation behind the player when not attacking, nice detail.
A bit too easy summoning the strongest unit all the time, could be more interesting if they had a bigger difference in soul cost and stats, so the player had to use each in different sutuations.
Has a few bugs: heroes get stuck on walls very often, doors can open when only one enemy was defeated and upgrade text doesn't fit fully.
But it's still really fun. With a bit of polishing, I could totally see it as a full game!