Could do with a bit of work.
Well... the game play was slightly enjoyable. You asked for a review on the coding/game play instead of visuals, so here goes.
The game play was under par. These styles of games are only good if there is some coherent award at the end or to continue from it. In this case, there is no story, and you just jump into killing something for no reason. People need excitement, so try and think of a reason.
I suggest the leveling up aspect of the game. A walking environment would also benefit the game. This would give it more interactivity and better game play, it would also allow you to work on that storyline.
I do enjoy the last second attacks by clicking on the yellow dots. This could be increased if they moved about randomly, to give it more skill requirement. This would let the user incorporate their skill and not just the that of the coding.
Overall the game could use some work, if you make a story line, walk able environment and extra attacks... you could really make a good game!
Good luck!