It looks pretty good, so far. But there's a few tweaks you might consider.
For the background of the cards, consider lightening up the faux aging effect. I know you want it to look like ye olde parchment, but that same effect takes away from the impact of your art.
Refine the art more - perhaps give it drawn backgrounds, to give the elements you're presenting some context. You might even consider just a splash of color, for greater visual appeal.
The back design really needs some work - some cleaning up, and perhaps even some symmetry. It looks like the doodles of an LotR fan in the high school art club on the cover of his binder. Maybe something that really lends to the "adventure" theme - a map of a valley or a map of a dungeon? Perhaps a castle on the top, a flipped image of the castle on the bottom, and a moat in the center to give you the rotational symmetry that would make this more appealing to buyers.