Fun and addictive, but I can't figure out what determines whether an attack hits or not. I'll shoot grenade after grenade at the walkers just to have them disappear as they get near.
I've gotten gold stars on everything except for Destroy 4 and the boss run. The boss run I'm just doing too slow, but I can't figure out for the life of me what I'm doing wrong on the other map.
Gotta say the ninja are my favorite unit, mostly 'cause of their versatility. They can hit things at range, melee them to death, and even run in for a surgical freeze strike to relieve your enemy of their ranged units.