That's the program in which I do all my works.
If you get the ArtRage 3.5 Pro edition (it's not that expensive considering what you get in return, I might say it's rather cheap!) you are basically set for life with one incredible painting tool.
Possibility to export your work on layers in PSD format is another mayor plus, since you can finalize your art in PS and that gives you some amazing results.
Pro version can even use PS filters & plugins directly from PS plugin directory.
Very fine tool indeed.