Suggestions and bug reports:
-I'd drop the "move the mouse to the edge of the viewport to move it" aesthetic. It works well for non-game programs and RTS games, but not so much casual card games. You should probably widen the window (or shrink the tiles) until the player can see the entire playing field. Any computer capable of running this will have at least an 800x600 display, so you might as well make the window a little larger.
-The game won't let me buy something that would put me at zero money.
-I'm not sure whether I just selected a bunch of cripplingly expensive cards, but I couldn't place anything on my first turn. You might want to give each player a token amount of money to get the ball rolling.
-When playing against an AI, my cards are hidden unless I mouse over them. Presumably this is a holdover from the two-player version of the game.
-It would be nice to be able to see the special abilities of an enemy unit when I mouseover them. Some of the special effects are pretty bewildering unless you're familiar with all of the cards. I'd advise displaying an entire card when the unit is moused over, rather than just a small tooltip.
-Speaking of mouseover, it seems to be a little broken, at least for enemy units. The tooltip and the enemy's movement range seem to be displayed randomly rather than consistently.
-The A/S/C/R identifiers for the statistics aren't very intuitive. Might want to replace them with little symbols. A sword, an arrow, crossed swords and a pawprint, maybe?