This game is great!
There are a couple of little things you could do to make it a little harder- once you have broken a hole in the first line of defence its game over because the pak's can't rotate... If you made it so once you were outside their firing arc they SLOWLY repositioned to face you then you would still have the element of flanking without it making the game too easy.
Similarly with enemy tanks- once you get the range upgrades they just sit there taking a pounding, once they get hit they should rotate until their front armour is pointing in the direction of the shot and then start moving towards the enemy until they are in range and fire back.
Other than that great game
Land Leveling Tip: Double Click 'Up' and one 'Down' Click is the same as nine small 'Up' Clicks- you get more land for your clicks!
This can even stack, so triple 'Up' click, followed by double 'down' click, followed by single 'up' click will give you massive tracts of land for only a few clicks