hi Komica ,
Yes i am the GPS creator and maker of Ramon set,nice to meet you.
I see your pictures and there is not a real difference in terms of quality. so you can paint probably batter on Gimp due his color selector. much more complex than PS. btw i like your characters, i dont know why, but they are not boring. maybe you could have a better pictures taking care of edges. There are hard , soft, crispy edges and the combination of these gives you more than the all fuzzy edges. imho.
Well, this is not the right forum for GIMP but , sorry Maxy there we go a bit of Spam! XD
Gimp is a very very interesting software and you are very lucky because the new BETA of GPS 1.5 is available . http://code.google.com/p/gps-gimp-paint-studio/downloads/detail?name=GPS_1_5_0_beta_release.zip&can=2&q=
it has lot of new things. that can´t be covered right here .but i tell you that GPS is doing a massive use of something called GimpPainter which is a fork of gimp that can be downloaded from..http://sourceforge.jp/projects/gimp-painter/releases/?package_id=6799/
so if you added GPS to the GImpPainter you will have acomplete suite for painting for FREE. nice uh?
anyquestions to my mail. take care.