While MMOs aren't their only bread and butter, NCsoft are certainly well known for their PC presence and when their attention swings around to the iOS it's hard not to take notice. Gem Keeper is their first swing at gaming on iDevices and much as you'd expect from a company with this much clout, it's a visually spectacular game to behold, but instead of an expected RPG they've gone for the safe bet of a tower defense game.

Thankfully Gem Keeper isn't entirely lost in the melange of titles already available as it introduces a 'rail' system, with towers able to be positioned not only on fixed points available around the map, but also on top of special slots on a sliding rail. The simple inclusion of such a system has huge implications for the gameplay (especially at higher levels) as players prioritize powerful towers to these spots to manually move and keep marauding monsters in range for as long as possible.

There are three areas in the main campaign mode, all designed to teach you how to operate and get the most out of each new tower (currently 14 in total). Aside from the usual set of towers, Gem Keeper tries to mix things up by changing how they feel - for instance, the typical 'linear piercing' tower is replaced by a sort of explosive bowling-ball. They're neat touches, but it's hard to shake the feeling of having done all this before.

This may be in part thanks to the smooth way in which the campaign progresses, making it a perfect introduction to the genre for those who are yet to dip their toes in to tower defense games. Three difficulties are on offer, with Easy geared towards absolutely new players, while Normal and Hard scale things up appropriately for return players or hardcore fans respectively.

The best that can be said of Gem Keeper is that it's a highly polished tower defense game - from its slick cartoonish designs that are easy to distinguish, to the simple mix of towers and level layouts that encourage varied approaches for reaching that final wave of creeps.

If you've had your fill of basic tower defense games, Gem Keeper may not be up to your speed, but it's definitely worth a look if you're a hardcore fan after something a little different or even a new player who wants to be eased in slowly.