I really love the choice of the subject, being an avid bird lover, especially of corvid family. I like the simplicity of the cityscape and the choice to put the focal point towards the right side of the painting.
The only things I feel to point out is the hue of the cityscape, the limited colour palette of the sky and clouds make it stand out not so effectively despite buildings are visible and distinguishable. The shades on the bottom part of the cloud follow too much the basic hue of the sky. Maybe working with complementary colours would add a bit of chromatic variety. Despite this I really like the lighter outline on the top of the cloud because it's receiving light from above. I also understand that you wanted to focus on the bird rather the bg, so it's a valid choice.
Another element I feel makes the composition fall flat in terms of colours is the lack of shading on the branch where the raven is perching. I see the different brown hues on it but I don't see for example the shade thrown by the bird. This would have added more realism to the composition. I like how the branch colour stands out the blue environment though.
Despite this nitpicking (hence my 4.5 vote), I really like the overall structure, each part is unique if the Rule of Thirds is used and the raven is beautiful. Nice details, shading and highlights. I like his/her pose too because it feels natural and that's how ravens would turn their head if they notice something that catches their interests. I know that pixel art can be challenging and painting with it can be even more challenging so I commend you for this variety of subject. Your gallery is really cool and I like your geometric style, so keep it up!