Hmm, well I havn't seen the original artwork, but I guess that means that I can have un-biased critique that you seem to want

The actual outline of the balloon seems a little jagged, since I too use a mouse, I know how hard it can be to draw smooth, natural curves on such objects (I get that a lot when I draw my fan-art, but it's not so bad with landscapes and space-art) I can see you have discovered the "ploygonal lassoo" trick that I use, if so, then it's a bit too evident around the top-left as I can see "corners". Perhaps more clicks which are closer together may take longer, but will get smoother results...But it's advisable to try out the pen-tool for such things

As for shading, which is a key ingredient, well, not too bad, but perhaps a little weak and "flat" looking. Make the highlighted areas brighter, and the shadowed areas darker. For shadows, I usually choose a darler, desaturated version of the "base colour" I'm shading, and set the brush to Multiply and brush a few times until it's dark enough. For highlighted areas, I choose a ligher version of the colour and set it to Screen mode. What really tops it off is "backlighting". That is, adding a highlight just on the edge of the shadowed side to represent ambient light from the surroundings...give it a colour depending on the surroundings, I'll use this as an example from mine [link] See how the shadowed sides aren't completely dark, but rather they have a blue highlight around the edges? that's what you can add here on the far right of all parts of the balloon.

Oh, and things such as fire, lighting, nebulae or other special effects that glow, use the brushes on either Linear dodge or Colour dodge mode, and you'll see it looks really cool when used with different colours, and each time you brush over it, it gets brighter, represent a stronger glow coming from the main source in the middle

Hope that was informative (man, I should be getting paid for this )

--
Old mother Hupboard went to the cupboard to fetch her poor dog a bone.
When she bent over, Rover took over and gave her a bone of his own.

yeah man, thanks a bunch! i would pay you but i have no money.
lol. but i'm gonna keep working on it.
i think my new one, white room lost man, is a bit better.

--
Sexy art --> [link]

"I am Vigori "