If you've never played Anomaly Warzone Earth, it's worth looking into - the game took the tower defense genre and turned it on its head, quite literally. Anomaly is a tower offense game, in which you send in and guide your forces through a defense-laden map and achieve various objects in the process. The sequel to that game is now out - Anomaly Korea.
The gameplay looks basically similar (though I'm certain there are some new features), so players of the previous game should have no problem jumping right in. The screenshots suggest visuals have been improved as well. The game is on sale for a promotional launch price of $2.99 (we're uncertain what the regular price will be), so now's the time to get it.