Nice concept! Suggestions: first levels slower and with one or two colors only (add more later), enemies on the very right (coming closer slowly), some way to connect keys with colors (labels etc)
Be careful with background colours. Somethimes they are too similar to the block/bubble balls and it's confusing. Also, draw a line for water surface in snow levels. It's impossible to know where the water stops. Great game! 4/5
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