You can imagine my surprise when yet another tower defence game arrived on the App Store, promising new levels of ingenuity and entertainment. Indeed, I was so surprised, I almost fell right back to sleep.

Accounting for your precious flock of sheep in TowerMadness means staying wide awake for this intense strategy game. Alien invaders intending to nab your woollen trophies in order to knit a scarf for their emperor mean building up defences.

If you can cut through the quirk and thwart the required number of attacking alien regiments with just one sheep left in your field, you win.

Most levels have several landing sites for the alien units, so you need to defend against a few different attack patterns. The aliens aren’t following a predefined path to your base.

Placing your defences about the map is far more strategic than simply lining the edges of the a predetermined route. Instead, you must try to create a winding path that slows the alien’s progress while subjecting them to as much defensive fire as possible.

There's a huge number of upgradable weapons, and an equally diverse number of aliens. Some are able to fly over your defences, meaning you need a good supply of anti-air weaponry to quickly take care of attackers who aren’t restricted by your fortifications. Others are essentially boss battles with a single, giant alien lumbering across the map.

Weapons are upgradable in real-time, but you need to choose the moment of enhancement carefully. During the upgrade process, the tower becomes momentarily unavailable.

The more significant the upgrade, the longer it’s out of commission. There’s a strong temptation to boost a tower’s power when a brawny alien approaches, though by then it’s often too late.

The 3D graphics are as impressive as the game's strategic depth. There’s no slow-down or dropped frames during the most chaotic moments when dozens of aliens fill the screen. It's quite impressive considering you can use pinch and pull gestures to zoom in from a bird’s eye view of the whole battle field to an eye level perspective with the aliens walking right at you.

Although the game features spatial stereo to add a little depth to the few sound effects, it’s rather mute, which is a shame. A little background music and some additional, humorous alien yelps could help lift TowerMadness off the screen a bit more (also, the title is rubbish).

Pin-pointing what sets TowerMadness apart from a genre full of mediocre efforts is difficult. It’s really a combination of depth and polish. Even though you might have two or three tower defence games already littering your iPhone home screen, it comes highly recommended.