its too easy
really, all you need is the walls filled with archers/cannoneers + keep upgrading the speed at which your tower fires. Also, put 2 cannon towers and 1 uuber tower right in front of the gate and thats about all it takes, dont waste money on recruits (other than the afore mentioned archers and cannoneers). any more than 3 towers is a waste, just use the money to upgrade the existing ones.
i liked the graphics and the game-play was simple but enjoyable. the money wasnt too much of a problem, but it would be nice if the recruits could be a bit stronger, because they just die after one hit from the creeps at later levels. But that might have been on purpose, seeing as how everything else is pretty damn strong.
an increase in the difficulty and a few extra towers would be really cool, or possibly making a PvP mode. also, possibly having archers that aren't on the wall. but overall, its an okay game, and worth a 6.5 (but not a 7) but there isnt one, hope to see another installment soon.