About the game:
Am I missing some options, or is it often impossible to hit the target even if you were able to know ahead of time which cards you'll be dealt?
Sometimes I get nothing but addition and subtraction cards which makes the game uninteresting (since the order they are placed in makes no difference to the result of the sum.)
What's the blue card for? I see the text "Hit my mini goal in 3 tries for a blue bonus card" in your 2-25 update, but I've not seen it in the actual game?
About the pixels:
To make it look more interesting, you need more of a theme for this - currently you've got a very simple red/white/yellow colour scheme with a quite minimalistic approach to the design. (Also, the faces don't really fit with the cards.) There's nothing wrong with that as such, but it's just not very exciting. At least try experimenting with different colours (especially less saturated ones, and remember you don't have to work on a white background.) Or think about adding a picture/design to the cards to use some of the empty space on them.
Put some details on the back of the cards - currently they're bright red and completely plain.
It would also look more interesting if you made the face-down pile of cards visibly a pile - i.e. give it some depth so you can see it's not just one face-down card.
I noticed that you're using 46 different colours in your image - this is quite excessive, and just makes it harder to work with. Some of your AA is basically invisible (e.g. between the white BG and the pale grey you're using behind the small text) and there are several almost indistinguishable colours in there (I didn't even realise there were 3 shades of red there until I looked in an editor). In fact, I'd suggest not bothering to do any AA until you're happy with the design, else it's just making it harder to edit.
Here's an edit just to give you some ideas - I'm not suggesting that this is the way you should be going, particularly.:

Also, check out this thread if you haven't already:
http://www.wayofthepixel.net/pixelation/index.php?topic=5848.0