This wallpaper is good for a first attempt at walling. My complaint with this wallpaper is that the extraction doesn't look as smooth on some areas, especially on her hair, ears, and tail. You can see some jagged edges. I might not have noticed this on my LCD screen at home though because it's so bright, but since I'm at campus, I can see the jagged edges. But then again as I look at it closer, it might due to the image being resized up from a smaller source. You linked to the original scan and it was much clearer but smaller than the scan used in your wallpaper. So my only guess is that you resized the scan up so that it would fit with the 1600x1200 resolution. Correct me if I'm wrong. It's just that the scan is only average in quality since it could have been clearer, crisper, and smoother.

As for the background, it looks cute. However, it is a bit repetitive and simple. Simple is good (I'm not saying it's bad), but you can achieve simplicity without making it look repetitive. I'm not sure if the stars are made manually by you or from brushes. If they are made by you, great job with that! I like the right side of wall with the rectangles better than the stars though. Overall, this wallpaper is great for your first try. I'm sure you will improve if you keep this up!