The same urge to snap a ruler in half or hurl a compass when facing the frustrations of high school geometry is channelled through geoDefense Swarm. This striking tower defence game takes a creative angle with open levels, but fails to measure up with flawed, often aggravating gameplay.

Destroying the geometric creeps that scurry across the screen is a matter of tactically plunking down towers. Unlike the first games that limited tower construction along set paths, geoDefense Swarm organises the screen into a grid of hexagonal tiles onto which towers can be placed. By devising intricate tower formations, you're able to direct the flow of enemies as they make a rush for the exit.

Devising complex mazes has the benefit of extending the time it takes for enemies to reach the exit, while at the same time whittling away their health. The former proves an entirely different tactical consideration from the latter. Understanding how to deploy each of the game's seven tower types is just as critical to destroying creeps as is delaying their trip to the exit.

It's a brilliant concept because it compels you to think about the position and type of each tower you buy in a meaningful way. One poorly placed or ill-considered tower can result in creeps leaking out of a carefully arranged maze or making it to the exit alive.

Figuring out how to arrange towers to best corral creeps is fairly easy, though actually defeating the swarms is a problem. Balancing issues contribute to an excessive level of difficulty. It stems in part from unreliable tower AI, but mostly it's the result of mediocre level design.

Towers routinely fail to target creeps. Crimson missile towers, for example, regularly fire rockets away from enemies. Rather than honing in on creeps, missiles can be seen looping several times before finally zeroing in on a foe or, worse yet, flying in the opposite direction off the screen.

Laser towers are entirely too fickle, following the lead creep of a wave even when they can fire on a line of enemies or destroy a weakened one.

Dealing with these quirks isn't nearly as aggravating as the levels themselves. Variations in the cost of towers and upgrades between levels are intended to push you toward specific tactics, but the lack of uniformity is confusing. This also has the effect of raising the already excessive difficulty.

While most levels begin with a few modest waves, things quickly spin out of control as enormous lines of creeps snake across the screen. Limited resources make it extremely difficult to adequately prepare for such onslaughts.

Even when resorting to tedious trial and error to discern the best combination of towers and upgrades to get the job done, some levels still frustrate.

By nature tower defence requires trial and error and experimentation, but geoDefense Swarm takes it to an extreme. The dazzling effect evoked by the game's gorgeous neon graphics and open levels is countered by flawed, frustratingly difficult gameplay.