A good start.
I actually kind of like the game as it is. However, I do agree that it would be pretty sweet if someone did team up with the creator and made a more polished and fancy version.
Unfortunately, a full game may be a long way off, or maybe even out of the question as far as Bunnykill's creator is concerned. So, in the meantime, here are a few things you could do to improve what is already created.
-Ranged Weapons. Guns were used quite a bit in the Bunnykill series, so it wouldn't be out of the question to give you the option of fighting with a gun.
-More Attacks. I get bored kicking and slashing my way through the same bunnies over and over. Maybe some sort of special attack or something would fix that.
-Healing. Maybe you could heal a few points in between rounds, or pick up a powerup every once in a while.
-Active Guarding. There is only one game I have ever played that did an acceptable job implementing passive guarding, and that is Tekken 5, a console game. It's far more complicated and deep than this "short and basic game," and was only able to pull it off because of several other faces of gameplay. It is not recommended here in a simple flash game.
-Interactive Environments. I would like to be able to move to different areas and all that good stuff, and I'd love to be able to damage walls and jump off of stuff. Most good fighting games have that.
Anyway, good job. 7/10. 4/5