I hate to be that guy, but in my opinion, with very few exceptions, the card art in Dominion is really, really bad. Much looks like amateurs trying too hard, like art students who aren't quite making it. The detail is sloppy, the perspective is off, and the proportions and colors aren't sufficiently correct to qualify as impressionistic. The figures and faces are painful to behold. Even art trying to be "cartoonish" has to have correct minimal elements, and they rarely are. Of the card art posted, for example, only Noble Brigand looks like it was done by a professional.
Compare the cards to other professional commercial artists; anything from book covers to (modern) Magic cards. Dominion art is just not good.
And yes, faces and figures are very hard. For a wall mural, I would strongly recommend simply the logo and a landscape, which is much easier to pull off, such as the Hinterlands cover, Feodum, Island, etc. Calm, serene, and nothing to stare at you.