Good game, liked the art style. Good enemy and boss design, they telegraphed their actions well so I could prepare for them. At one point it bugged and I went backwards from the fourth screen to the 1st screen of the level and I thought it was a good convenience, but as I played backtracking didn't do that again. You are incentivizing the player to backtrack with the upgrades that can't afford, so backtracking needs to be interesting not a slog.