Tower Defense games are one of the few genres that the iPhone excels at, and Star Defense, with an entirely fresh 3D take on the concept, multitouch, varied levels and multiplayer, is about as good as they get.
Instead of marching baddies across a 2D plane, Star Defense applies its traditional tower defense sensibilities to 3D worlds. At first the pacing can feel a little slow compared to the defense games you grew up with, but rest assured: things get sloppy, and your base will be destroyed. Plus, hey, good games are almost never this cheap.
From The App Developers: Use multitouch to spin and zoom entire worlds in Star Defense, the highly-anticipated strategy title created exclusively for the iPhone and iPod touch. Maximize your recon and plan carefully – each planet has unique pathways to protect, weapons to deploy, and enemies to overcome.
Survival depends on your ability to respond to the S'rath invaders in real time and build a mixture of towers that counteract all known alien units and resistances.