I love these kinds of games, but needs some work
First off, let me say that I love the concept. Also the level of historical detail you put in is really great! The complexity of the game isn't so great that it gets confusing, but is still engaging enough to present a challenge. Maybe you could add a multiplayer mode next?
The problem comes from the system of blocking cards. If the color of cards are matched up on each side, there is often nothing you can do. The opponent (or you) can block each move as it is played, no matter what order. This is of course if you happen to have the right combination. I'm just saying its frustrating when it happens. Not necessarily a game breaking problem, but one which warrants further examination. Maybe you could try to implement a system of hitpoints, such as in the Magic card game, where an attack can be partially blocked. It's just a thought. This would only apply to the scoring cards obviously.
Presentation: The graphics for the cards were nice, being photographs in most cases. Try getting a picture for the 88mm flak gun too, because the little pixel picture doesn't look as good. If you made the whole thing a LITTLE bigger in general, the info on the left hand side of the screen would be easier to read. Also, maybe change the graphic for the Block action, as it looks somewhat boring. Maybe put the word in front of an explosion or something?
Lastly, sound. Maybe a simple looping track to liven things up? Also, some sound effects for attacking and blocking etc. Intelligence cards can sound like a radio, air force cards sound like planes, ship cards sound like naval guns, ground cards sound like tanks, whatever you want to do. I think it would make the game much more exciting.
I hope to see a sequel! Maybe on the Italian front, or the Pacific! I feel you have a solid game here, it just needs a little examination of the mechanics and a few frills in the form of sounds and you'll be good to go!