Sure, the towers are mostly rehashes of the standard cadre, but the "power cores" that players must defend put an interesting twist on the strategic side of things. The cores are carried off by enemy mechs in ones and twos, and if a core-carrying unit is destroyed, it floats back towards the base--until it's picked up by another unit. This domino effect can lead to some intense reactionary tower building--that can often make for some terrible long-term ramifications. Created by Age of Empires II lead designer Mark Terrano, Defense Grid is at least worth a spin--especially if you're not familiar with the tower defense genre. Grab the demo here from FileShack. The PC game sells for $19.99 on Steam.