Airbag

[Devicho]

Not only is the lineart very jagged, but the shading contradicts itself and the colors are too close to the MS Paint defaults for my liking. On the box, the lightsource seems to come from the right, while on the enemy itself it's coming from the left. The lineart needs to be smoothed out, and in some places it doesn't even connect completely. I'm going to assume you're using the circle tool and resizing it when need be, which is a bad idea. Make the circle from scratch, it will come out much better. As for the colors, try experimenting more with custom colors instead of lightening and darkening defaults, which it looks like you did.

Fix up those issues and it will look much nicer.