Mediocre at best
1. It's FAR too easy. Every level can be beaten by sending a continuous stream of archers, and once you've upgraded enough times, it's impossible to send all of them before the castle dies.
2. Infantry are worthless. Archers can only be picked off one at a time, and with less than 100% accuracy. Infantry have to survive the journey to the wall, first of all, and then get wiped out periodically at the wall, and that can't miss.
Never got to try the other units. After I beat Level 10 in about 15 second, I quit.
Given that the graphics and style aren't enough to compensate for the terrible gameplay, I can't rate this very high at all.