Tower defence games can be found in abundance on the App Store, with many that try out new ideas. Star Defense is one of the latest additions to this fast expanding category of games, and the twist here is that of full 3D environments. We haven't played such a game like this one, and although it can be aggravating at times, it's certainly one that we'd recommend.

So how do you do a full 3D tower defense game on the iPhone? Cleverly, the developer has decided to place the action on a planetary scale. This means that whilst you can pinch to zoom in and out, you'll never see the whole landscape at once. Instead, you'll have to explore the terrain yourself to see exactly where the best tower placement is. Some scenarios involve big metal cubes, so you'll be glad to know that each tower's range is 3D in nature, too.

Each map has a variety of S'rath that you must eliminate. Some can be resistant to certain types of towers, so effective strategies rely on utilising each of the five towers at your disposal. You won't be granted all of these at the start, but they are unlocked later on once you've successfully ridden the planet of creeps. In most cases, the best placement is either corners or pathways where you have an opportunity to hit the S'rath twice - utilising slow towers on corners can prove deadly for the faster enemies, but don't rely on them for heavier creeps because they are often immune.

Along the way, you'll often pick up achievements, known as commendations in the game. These range from easy (have three waves on screen at once), to hard (complete all planets on hard), to long haul commendations that reward you for investing a lot of time into the game (kill 1,000 of each enemy). It's a good incentive to keep on playing the game long after you've beaten each map.

Gameplay wise, the game has a few problems. Sometimes, the difficulty can ramp up unexpectedly, and it seems the controls are built for the opposite scenario. It can get frustrating when you're trying to either quickly upgrade a tower, or dragging one out onto the field to place it. But, a nice touch is that you can speed up the next wave by tapping the preview of it - this will also list if a wave has a resistance to a certain tower.

Visually, the game is very impressive.

Visually, the game is very impressive. The sci-fi theme is seen throughout, with fantastic attention to detail. The 3D in game is really good, and the objects are quite detailed. The same can't be said for the gorgeous, yet pixellated backdrops - there are a few places where you could just wish for a higher resolution texture. The sound effects are extremely well done, as is the music - a calm ambience that adds atmosphere and tension to the proceedings.

Star Defense is a well executed Tower Defence game. It looks great, it's tough to beat, and it has excellent social networking features - Twitter challenges, facebook connect and the new ngmoco plus+ connectivity. But it's not a revolutionary game - indeed, there are more full featured 2D Tower Defence games with far more strategic possibilities. For your first taste of the genre though, this may be the best introduction - especially when you will be able to download new content for it. It's pricey for the App Store, but it's worth it.

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