I love it! Some (okay, two) small suggestions:
- A little indicator (flashing arrow or something) showing where an enemy is going to spawn might be helpful in reducing the 'BS' deaths - this was the only thing I really wished was already in the game
- If you were able to jump for a fraction of a second after running off an edge, I think it would make jumping feel a little nicer! I'm pretty sure games like Super Mario did the same, but I'm also not sure if it would make deaths from falling off the screen non-existent. I'm also not 100% you don't do this, it just doesn't feel like it to me!
Other than that, I have no complaints! You could definitely expand this to having multiple modes (zombies-like survival mode with waves of enemies, timed mode for more difficulty, maybe even different samurais) if you'd like - however I think it's also super cool how it is!