Defense Technica is a tower defence game which harks backs to early entries in the genre. While many modern TD games send enemies stomping towards you along pre-determined paths, Defense Technica makes you use your own towers to steer and funnel your enemies where you want them.

This old-skool formula is married with a card system that acts as a replacement for tower upgrades. Though these cards - which are bought via IAPs - are supposed to be an optional feature, the game does a very good job of making you dependant on free features that it decides to charge for later.

Take the Eagle Eye system, for example. It shows you the optimum path down which  to direct incoming enemies via a green arrow. You'll want to use barricades or towers to block off the yellow and red arrow paths to give yourself the most breathing room. Eagle Eye is not essential, but seeing that it's free and so helpful, you soon become reliant. It's at that point that the game begins to charge you for it.

Your initial towers include a machine gun and a melee claw tower, with the more interesting and expensive towers unlocked by gaining the right card. You have to be careful when destroying blocks to make room in case you inadvertently hand the invading a clear path to victory. You can simply replace barricades with towers if you need additional fire-power, but it always seems that you're second guessing your placement, which can be problematic in the heat of battle.

Meanwhile, the upgrade cards - which cost a large amount of the in-app currency of crystals - are essentially random acquisitions. You pay for packs, and the cards may lower tower cost or speed up wealth, or even grant you a new tower. There's no way to predict what you'll receive, and it feels like more of a hindrance than a useful addition to the game.

Since the cards and crystals inform Defence Technica's design, you wind up with a game that leaves a skightly bitter taste in you mouth. The way the developers have approached the path-building is admirable, and might be enough to warrant a purchase, but only to the most dedicated tower defence players.