Sweet game! here some quick feedback on things i would implement.
a death animation that plays before you respawn.
more control options i dont mean remapping controls or any of that hard stuff. i would just add up as a jump button as well so the game can be played one handed. and while your at it add WASD as well :)
i would like to select level without using the mouse. (could add an overworld with portals or something)
i did not get who the stars were for but nice partical effects when collected.