Kingdom Rush remains one of the best examples of a game perfectly suited to Apple's iOS platform — it's an attractive tower defense game well-suited for quick sessions while on the go, but addictive enough to make you want to spend hours on it. Now, Ironhide Game Studio has released its sequel, Kingdom Rush Frontiers, for both the iPhone ($2.99) and iPad ($4.99). While the gameplay looks quite similar to its predecessor, Frontiers has been beefed up with a variety of new tools at your disposal, including eight new towers, nine total legendary heroes, new boss fights, and "over 18" total tower abilities. The bad guys got an upgrade, too — there's a total of 40 different enemies trying to get past your hopefully clever defenses. We haven't had a chance yet to try the game out ourselves, but given the quality of its predecssor, Frontiers should definitely be worth a look if you're in the mood for a new tower defense game. If you're on the fence, check out the trailer below.