There are dozens if not hundreds of tower defense games on the App Store, but for my money, Kingdom Rush is just about the best of them. It's originally a Flash game that's found a lot of success on iOS, and after a few solid content-filled updates, it now features tons of levels, enemies, units to buy and upgrades to earn as you play along through the game.
And there's even more on the way. Kingdom Rush: Frontiers is a new version of the game due out this spring, and it's received a teaser trailer of its own, which you can watch below. As you can see, the teaser promises some more exotic heroes and enemies, and Ironhide Game Studio has hinted that the game will do a little underground plundering as well. If you've never played Kingdom Rush, do yourself a favorite and pick up the current US$0.99 title right away, and we'll keep an eye out for Frontiers later on this spring.