The story is good, and presented well. The slime animation is smooth, and I like the art, but it makes me a bit sad that you used open source art. (I like seeing custom art, that's all! :D) The gameplay is addicting, but the random hero drop made some challenges nearly impossible. I didn't even know I could attack until my friend pointed out the button in the bottom-right! And I didn't know that right-arrow was attack until I literally just looked up at the game!
The win conditions make me sad. "Make a score of thirty to win"? I haven't "won" yet, but that kinda reduces the story to me. I think this would be the type of game as a endless runner-thing, with online high scores. Maybe you could have achievements in the future for reaching a certain number, or a "pacifist" achievement for jumping over a certain number of heroes? Just some ideas.
I also applaud your efforts to make the game touchscreen-friendly; I'm trying to do that with my C2 Jam entry now, and it's nice to see you succeeded! Also, I didn't encounter any bugs during my playthrough (at least, none I'm aware of).