Moving up the ranks takes time and patience. I am at Colonel now and have been playing for a week. The ranks take progressively more points to level up, b/c in theory you should be getting better as you go along and should be able to rack up a bigger score. Tanks are good when used properly. They don't serve well as offense but are amazing for defense. Put your guys under a tank and they are untouchable.
never mind that last post, I am an idiot and did not read the card completely, and apparently I am incredibly unlucky when it comes to that particular card.
I also received the "hard" badge prematurely. I got it after beating just the first part of stage 1. But other than the err with the badge it is a pretty good game.
 "Frantic")
 "Mud and Blood 2")
 "Whiteboard Tower Defense")
 "The Necronomicon")
 "Achilles")
 "Epic war")