It may be due to the fact Im a huge fan of ArtRage Studio Pro (the full, home-computer version) that Im only mildly impressed with this iPhone/iPad version.
The brushes are limited but nice where they apply. Paint thickness is limited, too. Id also like to see the water color features of the PC version brought into the mobile version - theres a lot lacking when all you have for painting is oil.
However, having said that the features that are present are fantastic and very true to the full version. I wish I could apply more "paint thinner" options and would expect water-color to be the same (with water).
So, in closing, Id say this is a nice "diet" version of the full software and theres really no reason for it to be even on a mobile platform.
However, if Ambient Design decides to roll out the full spread of features to mobile... this may be one of the greatest painting programs out there because they *really* know how to do it well!
Dano in DSM about ArtRage for iPhone