I was able to spend a few minutes earlier today with Ngmoco's upcoming tower defense game, Star Defense and was pleasantly surprised with the iPhone game's potential.
Star Defense is a classic tower defense game set on a series of planets. Instead of defending your base from a line of encroaching enemies from a top-down perspective, though, the game plays in 3D.
The game will feature seven or so worlds that you unlock as you go and three difficulty settings. The locations I saw included a comet-like planet and a square Borgish cube. In both levels enemies spawned from an alien ship and then marched along a trail that wrapped around the planet or cube until arriving at your station.
The 3D perspective could be turned or zoomed into using the touch interface.
As of my playing the game has five levels, all upgradable. When placing when of these structures it shows the area it can shoot into with by shading the map. The game currently has a 30 tower per-a-level cap as well.
The high production value of the game and the interesting LittleBigPlanet aesthetic for the settings, seem to make the game different enough to warrant a buy, even from hard-core Fieldrunner fans.