I think it looks pretty static and lifeless.
You overemphasize vertical and horizontal lines and tha's why the result feels pretty static.
I mean you can use those principles for stuff which should be static, like houses.For characters which are alive iit's usually better to try to make them feel alive.
Even if it's a robot you can try to apply some realistic posing.
Try to capture some weight.
If people stand they usually have more weight on one foot.
It doesn't even need detail. All you need to improve can be done by the shilouette alone.
also make the gun aim in the direction the guy is shooting.
Also for a game the spritesize is incredible hug. I personally would not recommend to use sprites taller than 96 pixels.
