.:Robot Riot:.

Vision: The scene is self evident and highly dramatic, which is something you have a knack for. Being the American that I am, I love these sorts of actionesque scenes. The poses you chose are good at keeping things bracing, they are far from being boring. You did your best with these characters.
I have a quandary with your choice of scenery color closely resembling the skin color of the characters. It causes their presence to lose a bit of energy.

Originality: While I will award half a point for coming up with an original mood to contrast the quirky characters, the fact remains that they were not conceived by you.
Such is the way I score originality for this sort of thing.

Technique: I am impressed with your shading, but the position of the shadow is incorrect as far as the light source is concerned (the implied light source being the ray gun). The weapon Phineas is holding blends in with his outfit, which does not allow it to contribute much to the picture unlike his counterpart's weapon.
I acknowledge your astute technique, now all you have to do is implement it properly.

Impact: These things aside, the impact does not falter much at all. You did very well at placing these characters in a situation that draws the interest of viewers. I would contemplate scoring this higher if the backdrop was not skin-colored and a little more interesting.

Overall: While I don't watch the show, you've managed to capture my interest with this drawing. Remarkable work.