The tower defense and castle defense genres are quite popular on iOS. Touch devices work perfectly for that type of game and, as a result, it's hard for a new defense game to distinguish itself from the others. Battles and Castles has just been released and seems to have some interesting features that sets it apart.
The game seems to combine elements of traditional tower/castle defense games with building elements (that have become recently popular with games like Minecraft) and RPG elements. Users actually build their castles before defending them and then recruit units, find treasure, and explore mines. It seems to have elements that fans of nearly any genre can enjoy: strategy, simulation, action, and role-playing. The game has over 20 units and 20 buildings, three levels of technology, two campaign modes, multiplayer vs AI, local multiplayer on the device itself, and Game Center support.
Battles and Castles is a universal app and is available for $2.99.