It's very easy to tell what's a mimic and what's a regular treasure chest (and mimics can't move, so you can simply ignore them). This is a rather "classic" roguelike game, with a traditional exploration phase, so both learning and difficulty are rather common and needed in the genre. And the Chieftain was not a bug: as shown in the game, there's a "threat bar" that gets charged by defeating enemies, and when it's full it starts a strong boss fight.
The whole game project is meant to be a roguelike with some difficulty, I tried my best to tag with the correct tags and genres in order to clearly state the game's genre. Some games are supposed to be very simple, like idle/casual games, some others are meant to be harder.