Actually beautiful game
This is a masterclass in making use of a limitation/theme. At no time did the one bullet mechanic feel like a contrivance, it was always organic and original. The gameplay is simply amazing and epic, I felt really cool timing my jumps in order to create cool "set pieces".
What an astounding presentation too. Impeccable art, a cutscene, and all of it in 3 days? Wow.
If I have to say anything slightly negative about this little gem is that the dash got me killed more often than not, but I don't know whether that's a skill issue on my end. Also, enemy variety but I'm not going to pontificate here saying you needed a boss and more enemy types in a game made in 3 days lol.
All in all, you have an amazing product here with very solid core mechanics that if you wanted to, you could extend and release on many platforms, even smartphones. I would definitely play something like that!