Tons of potential.
Well.
I'm gonna start with the engine, seeing as that's where the issues lie. The gravity is way too high. I understand that this is so because the game is intended to be difficult, but I also understand that a game's objective is ultimately to be fun. I think this game would be a piss-ton more fun if the dude were lighter; even if that meant the platforms had to be further apart to retain then difficulty. That said, this game was a lot of fun once I'd gotten into it, but once I had died I didn't feel the engine itself was fun enough for me to go through all that again. The attacking mechanic -- on the other hand -- surpassed my expectations. I had assumed that it would follow suit with the amateurish feel of the jumping and be buggy with awful hitbox issues. I instead found the mechanic to be surprisingly smooth and lenient, so kudos on that front.
Now for the visuals. The art itself comes across rushed and unprofessional (although it would be bullshit for me to expect a free game to look professional), with unnecessary gradients and sloppy linework. The animation within that, however, is nicely done, with pleasing beheading physics and character movements that lie commendably on the good side of the simplistic/amateurish line that is often too fine for some animators to deal with. The menu screen is also well-presented.
As for the music...well..it's not really my place to critique.
All in all, a brilliant effort, and the results are not to be sniffed at considering this is your first flash. Not a total originality-fest, but most great artists start off copying someone else before they find their own way in their field, and I think you have a ton of potential.
Best of luck in the future,
-Grandmaster Roo.