Ngmoco has released a gameplay video of their upcoming Star Defense game. As a tower defense game, the gameplay should be roughly similar to Fieldrunners, The Creeps or 7 Cities.
The general goal for these games is to protect your base from wave-after-wave of enemies by building up tower defenses. You can traditionally purchase new towers based on money you receive from destroying the enemies.
Ngmoco has provided very few details of this game beyond an early screenshot and this video: