If you kill the two enemies before the end of level 1, you can't physically jump high enough to finish the level. That's bad game design. One solution would be to spawn another enemy if enemies == 0.

The hitboxes are too big compared to the sprites, the graphics are ugly and I'm not seeing anything particularly original or interesting here.

Pretty much a stickfigure-like-mario game. But it is enjoyable. The animations (jumping, running, etc.) could be slightly improved, but that's a 3.5 rating from me.