I can only confirm what people said before me <img src="smileys/smiley1.gif" border="0" align="middle" />, graphics look good to me, but couldn't figure out the attack system. I tried to kill the enemy but failed, couldn't get past him. He seemed to die, then he would explode(?) and kill me too.
I don't think the attack system itself is a problem, just its steep learning curve. I would say, try making a tutorial. First level you have to jump over some hole using cat jump, and guide the player how to do it as explicitly as possible and in as few words as possible - I found that players tend to ignore long text, best to keep it simple. No, VERY simple. Then next level practice the basic attack, then the "multiplied" attack etc.
I didn't notice any slowness either, constant 60 fps as far as I could tell.
Die on one hit is not good, people these days don't seem to have the patience they (we <img src="smileys/smiley4.gif" border="0" align="middle" />) when we played video games 20 years ago. If they can't figure out a game EASILY, they move to the next.
Also what I noticed is that people like to have a story of sorts going on, like who's this Froghead and why does he do what he does? And why does he look like a cat with a frog head?
HTH, and nice work!