Suggestions
You've got a good thing going here. However, the game is hobbled by a few major problems which make it an absolutely frustrating experience to play. It's always aggravating when a game has excellent polish and design, and then a handful of critical issues negate the entire gameplay experience because they are such gamebreakers.
First, knives thrown by enemies must be slowed as they travel through the air. The player moves quite fast, and the quickly scrolling screen combines with the non-descript animation of the flying knife to create a situation where it is irritatingly difficult to block knives with your sword. These problems are further compounded by three things:
1. the lack of a throwing animation by the enemies -- knives simply issue out from their bodies towards you, giving the player no clue to react.
2. the slow reload speed of the player's sword.
3. The hit-detection for the player seems to be quite a bit in front of his animation, instead of cleanly overlaid on top of him. This causes the player to swing once the knife is a "foot" or two in front of the player... at which point the player has already taken damage.
4. As mentioned above, knives are non-descript. Increase their size, brightness, color, or some combination thereof so that they may be seen and dealt with.
The speed overall should be reduced. This includes the walking speed of the player, enemies, and their respective projectiles. Jumping and subsequent movement in mid-air should be dramatically slowed down, so that the player can have a greater degree of control while ascending and landing.
A few major problems keep this from really "working" as a playable game.
Work on these things, and you'll have a great addition to Newgrounds!