Modern tower defense games for iOS

The tower defense genre started out with Desktop Tower Defense, a Flash game you could play in your Web browser, but once the iTunes App Store opened, developers quickly realized this kind of game was a perfect fit for iOS devices. Soon, tower defense games that are iOS classics emerged now, including GeoDefense, Fieldrunners, and the hugely popular Plants vs. Zombies. The touch-screen interface made iOS devices a natural platform for tower defense gaming, allowing you to place units with only a few taps of your finger easily, and the result was the perfect time-waster requiring both quick thinking and a solid strategy. Those early games are still fun even now, but the modern entries in the Tower Defense genre add even more to the action with 3D graphics, new types of gameplay, and new ways to take benefit of today's more powerful iOS devices. Whether you're a serious tower defense aficionado or new to the genre, you'll like the direction developers have taken with the tower defense games that are now available. This week's collection of iOS programs are all tower defense games. The first is the latest sequel to a popular franchise in which you take the fight to the alien homeworld for the final showdown. The second offers up crisp 3D graphics as you defend a flock of sheep from an onslaught of enemies. The last is a new game that takes a different angle, challenging you to become the invader against well-defended maps, using capabilities and units to keep your assault force alive. Place turrets on the path, but also be aware of your Commander (mech) who gives special abilities. Sentinel 3: Homeworld ($2.99 - Universal) is the latest installment (released late in 2010) of the Sentinel tower defense franchise, offering more units to choose from, new maps, and new talents 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 wish to add more levels and maps even. Sentinel 3: Homeworld starts you off slowly; you only get one type of unit plus a Commander that offers bonuses to close by 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 talents 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.