Did you use some kind of image tracer over the face? As you can probably see yourself, the program left some pretty horrible lines behind. The AA at the hair, for example, looks horrid. Also, learn about colors. These colours don't go well together at all.
Not bad for a day's work. Look into anti-aliasing and smoothing the edges, probably create a bit more of a shadow from his mask and hair to the background. Other than that, great job.