Just got the demo.Easy mode was easy to beat, Normal too, but I was stuck for 4-5 games on Hard. Then I passed it, and passed Insane on the next try (sacrificed a guy to win that one). I don't intend to try God.
Experience on the pico-8 version did help a lot. My winning strategy is : taking the Adventurer and use his key detection to rush. Stop to free prisoners. If a hero has enough life, spend extra money any time possible to avoid unnecessary levelling. Taking armor anytime possible (armor is much more balanced than in the pico-8 version, but still good).