It's clear that this is a work of love by the developer. Interesting art style, good game design, no micro-transactions, very fun to play. However, after a few hours of playing, once the best cards are unlocked, the game becomes too easy (even on the highest difficulties, Kraken & Random Sea).
It's such a fun game, but please, make it harder! With the endgame deck, I can play those levels with my eyes half-closed and still win 90% of the time.