Really cute concept. I was honestly drawn in by the weapon sprite and despite being quite simple it was still fun to use, it felt much longer than a normal sword. The music was pretty repetitive but I have to admit it grows on you and I felt myself zoning out listening to it (in a good way, very relaxing). The graphics themselves were very cleanly presented, nice contrast and very sharp. I'd say the game's presentation was its strongest suit.
Some feedback,
1. It took me a long time, like a ridiculously long time, to figure out how to jump. O seems like such a random keybinding to me. I tried to view the help screen from the menu but unfortunately it wasn't working, so I had to press most of the buttons on my keyboard before I figured it out. Once I did, the jump felt pretty good.
2. I ran into a gamebreaking bug where once I had unlocked double jump, I went back to the left side of the map to try to follow that upwards path, but double jumping on that platform didn't load the next screen and I ended up on the ceiling of the level. I eventually fell of and was unable to progress.
3. As has been mentioned, the losing of all progress and being sent back to the main menu on death is a pretty big bummer.
Definitely some cool stuff in here, but it needs some polish as well. Overall it was a pretty clean experience some minor annoyances aside.