Wow! This game is so complete in every sense! First of all, the theme fits so awesome. Just starting the game and hearing the first notes of the song, took me back to the classic computer games. The game feels very agile, and everything gave cool feedback. It's cool that it's about collecting coins because collecting them is very rewarding.
The variety of enemies is interesting and I liked the combination of getting rewarded for killing them, but they being slow enough to ignore, made it more relevant choosing when to fight.
The changing of scenery is also very cool. Moving between biomes changes the music and enemies, traps, so that ties really well together the classic theme with the mechanics of metroidvanias.
The difficulty was good, and the skill expression as well. The map system was amazing, overall this game is full of details that make for a very complete experience. If I had to choose something to improve, I'd make the text more responsive. Sometimes it feels a bit slow, or not clear when it responds to input and when it doesn't.