I’m terrible at, but love, tower defense style games.  I usually only play them on the PC (or sometimes the iPhone), but after playing the demo for Defense Grid: The Awakening on the XBox I stumped up the points for the full version.  Spent a few hours playing it on Sunday, and it’s really quite engaging.  So far, the levels have been easy enough to beat with only a few lost power cores at most, but challenging enough to keep me busy.