Wow, this is a really great prototype! The controls are great and smooth (although I would prefer the option of using WASD), and the combat is similar to the original Zelda in a challenging and strategic way.
My biggest gripe is that the enemies seem to move in a random direction with a random number pixels. I have found no success in changing this in my own experience, but it keeps the enemies pretty much stationary and not much of a challenge. Also, the boss's flames being more realistic was pretty jarring. I find it best to keep things stylistically consistent even if you can make it look better.
Overall, awesome start! I'd love to play the original game when it comes out if hasn't already!