It looks like there's too many random pixels everywhere. It just looks very messy and such. I like the overall design though, but do you think you could make it just smooth, or are you trying to go for a sandy effect?

Overall it is an interesting work. The shading is messy, but the grainy texture does give it an abstract look. However, it should be refined.

If you want to make it smoother, you should try using dither and anti-alias, like in this post. By carefully placing the colors you can shade the balloon softly.

If you did the "spray" texture on purpose, you should make it cleaner. For example, when we look closer, some edges on the blue circles are rough. Also, there are light pixels in the dark areas and dark pixels in the light areas. If you want to use this type of texture, you have to be careful about how messy it looks.


Here I've put the things I talked about in the red boxes. (Sorry for the big image!)

The tutorial in the link is very useful. It might be hard to understand if you use google translate, but please try your best. I think you have good ideas which will look very nice with more time.