I really like the art style. The silhouettes with the lighter hills and stuff in the background looks really cool. It would be even more awesome if it had a parallax effect though. The gameplay is really simple, but it's not bad. I would suggest giving some better feedback for when the player hits enemies (make them flash white or something like the boss does) so that they know their sword is actually doing something. As far as movement is concerned, I personally think the samurai could move a good bit faster (or add a sprint button) just to make the game feel a bit better and reduce time spent walking. The boss at the end was cool, but it felt almost impossible to move out of the attack area before getting attacked (though I do really like the indicator of when/where he's going to hit). It was also a bit weird that I get sent straight back to the title screen after killing the boss.
But overall, this is a pretty cool game that has a lot of potential with a few tweaks!