Sentinel 3: Homeworld is the latest installment (released late in 2010) of the Sentinel tower defense franchise, offering more units to choose from, new maps, and new abilities that help you stave off wave after wave of alien enemies. The interface is like many in the fixed-path tower defense genre, letting you drag and drop units on the edges of a path to fortify your defenses against each wave of enemies. Sentinel 3 comes with a 20-level, 14-map campaign and an endless mode, and also offers in-app purchases if you want to add even more levels and maps.
Sentinel 3: Homeworld starts you off slowly; you get one type of unit plus a Commander that offers bonuses to nearby units. As the game progresses you'll be able to unlock more than 20 turrets, orbital ship weapons, and automated drones. The unique Commander unit can be upgraded as well, and you'll need his higher stats and special abilities to defeat some of the higher-level assaults. Once you've unlocked a few units, you can plan for the coming invasion by setting up loadouts of units that will work best against specific types of enemies.
Overall, with new turret types, the addition of the Commander, four skill levels, OpenFeint support, and original music from Specimen A, Sentinel 3: Homeworld makes for an excellent addition to the franchise. Anyone who likes tower defense games will enjoy this well-polished title.