The first thing I notice is that the lines are very rough. Especially if you want to copy the style of Don Rosa, you should draw as detailed and exact as possible. The whole picture looks like it was made in Microsoft Paint. The next thing is the coloring: You missed the legs. That shouldn't happen when you put a picture up on deviantart, or, in fact, anywhere. But I can see potencial, just keep practacing and maybe one day you'll be as good as Barks or Vicar (I don't think anyone could get to Don's level, myself definitely included).