Below Average.
The flash is, practically a minigame. The graphics and animations are slightly above average, but they're still rigid and the sound is poor--perhaps some music would be nice. The game itself is incredibly repetitive. Without a story, objective, or background you won't find anything engaging in fighting aliens with a 4-legged glitchy robot. Thus, you'll lose interest pretty fast and forget this game like no alien invasion ever happened. The game is simplistic, I get the concept, but the execution is poorly done and doesn't have that long lasting impression.
It can be enjoyable, for a second, but seeing that you only progress through a few different enemies and only switching level backgrounds with no challenge or variety whatsoever, you'll find it all pointless. The big verdict is a 4/10, a poorly designed below average flash. Thank the graphics.