Survival is a mental struggle as much as it is a physical one. It's one thing to push your body to the limit hacking zombies up with a machete, but when the undead hordes are never-ending it's hard to stay motivated.

Zombie Attack! Second Wave slices up loosely structured tower defence gameplay that demands as much perseverance to stay interested in playing as it does for your stranded survivor to stay alive.

You take the role of a lone human in a world overrun by zombies. Across four locations - a ruined bridge, graveyard, trailer park, and backyard - you keep the undead at bay by building various turrets. Since zombies roam about each map freely, turret placement is of the utmost importance.

Preserving your mobile headquarters at the far end of the screen is your paramount objective, so your defences must be designed to ensure its integrity.

Basic turrets provide a defensive foundation. You've got rifle, cannon, and flamethrower varieties that behave predictably and effectively.

More exotic machinery is where all the fun is at, though. The rotating axe blades of the choppa turret hack zombies that stupidly amble in its attack range. Decoy turrets lure undead passersby with a mannequin only to strike at them when they approach.

Cash collected from dispatched zombies enables you to plop down new turrets. More importantly, however, you can upgrade your existing arsenal. Each turret can be levelled up to a maximum of six times, each level providing a boost in range and attack power.

Interestingly, the cost of upgrading turrets increases depending on the total number of turrets in play. As such, the more high level turrets you have, the more expensive it is to upgrade those turrets.

While seemingly unnecessary, it actually forces you to spend money wisely and consider each upgrade carefully. Not that it matters much because the cash starts flowing when enemies pour onto the screen at the highest levels of play.

It takes longer than desired for a game to get to that point, unfortunately. Zombie Attack! moves at a pace that tests your patience as much as it does your strategy. Survival mode encourages you to hold out for as long as possible in the hopes of posting a killer score online, yet the lofty goals of the supplemental Challenge mode play out in much the same way.

From sped-up zombies to restricting use of specific turrets, Challenge mode presents cool scenarios that take too long to crescendo. The path to each challenge's noted score objective is a long one. Shorter stages based on tough waves of zombies instead of a general score would give Challenges better structure and greater appeal. Right now, they feel as if they go on and on and on.

Persevere, though, and you're sure to find Zombie Attack! an amusing experience. Creative turrets and satisfying upgrades make it fun cutting up the undead masses, even if it the gameplay moves hardly faster than them.