Overall, it’s pretty good for a first try! The proportions definitely feel cute and you have a cool aesthetic there. The only proportional issue I see is that the arms may be a bit short. When your arms are straight, your fingers usually reach down to about midway down your thigh. You may want to consider making the gun a bit larger for more clarity and to help reinforce the cuteness of the character in comparison.
In regards to the composition, you may want to dim the snow on the ground a bit so that the logo pops out more in contrast and the background feels a bit more consistent in lighting level.
I agree with Strawberry on the rendering - you have some areas which look fuzzy or blurry due to having too many colors in certain areas. One area this is happening is the pants. You’re using what appears to be 4 shades to create the shading on the pants, but you really only need two. The colors you used to blend the light and shadow are redundant at this size and are causing banding (we can see individual bands of color in an area you’ve intended to look like a gradient).
While I understand the intent of trying to smooth areas out with many colors or add texture with dithering, I recommend trying to focus on how you can make your shadows into simple shapes which define the forms of your subject based on your light source. Currently, some areas of your character are lit from the side such as the pants, whereas other areas are lit from the top left such as the chest piece or muzzle of the mask. Try to make sure these forms are consistently lit from roughly the same angle and use as few colors as possible to start out with (if needed for detail, you can add in more colors as you go).
Once you’re comfortable with this, you can start thinking about more complicated concepts of how light interacts with different materials. Like Strawberry mentioned, metal is characterized by distinct dark and light areas. This would be good for metal which is polished and has a slick, reflective surface. Rough or dusty metal might have less clear reflections and a bit of texture to it with nicks in the surface and whatnot. Don’t be afraid to use reference photos or look at objects around you to study how you might approach rendering different materials.
Good luck and keep at it! This is good for only having started pixel art two weeks ago. Imagine what you could do in a few months or even a year if you keep practicing!