for those who follow the genre, there is one small innovation here which does add an interesting element of strategy: when enemies reach the base, they stay at the gate attacking it (rather than going in and eating one life). this actually has strategic implications because it means you can't just put all your attackers up front and "sacrifice" one life occasionally by letting an enemy get through the lines. with this twist it means that the less defenses you have at the end of the path, the more damage any attacker is going to cause if he sneaks through. nice touch.
