I’m a sucker for tower defense games. They all start from a simple premise: Bad guys are marching from point A to point B along a predetermined route, and you’re tasked with erecting towers to stop their progress.

Hidden Path Entertainment’s upcoming PC and Xbox 360 game Defense Grid: The Awakening takes the successful tower defense formula and expands upon it, offering all the cathartic pleasure to be had in strategically mowing down wave after wave of mindless critters in gorgeous, expansive environments.

In the future, humanity has narrowly beaten back the terrible onslaught of an alien race. With the menace decimated, we got lazy, and the grid that once defended our planet went unattended. Unsurprisingly, the aliens return and begin attacking the very system that thwarted their first advance. Instead of simply chewing through their ranks, you’ve got to stop them from stealing your power cores, the tiny floating orbs that power the entire defense network and keep your towers alive.

Sure, there are questions — why don’t monsters ever attack the towers directly, or just all charge in at once? — but let’s move beyond the why, and examine the how awesome.

During my recent hands-on with the PC version, I took some time to get acquainted with the alien menace, and came away impressed. As two objective passersby in the Wired offices noted, Defense Grid is Desktop Tower Defense but "sexy" and "pimped out," with clever enhancements that ramp up the challenge without completely overwhelming those unfamiliar to the genre.

Defense Grid is decidedly simple to pick up and play. There are a total of ten towers that you can erect. The simplest are armed with flamethrowers and machine guns. And then there are the powerful ones, like a Meteor tower that launches a massive explosive blast, or the Tesla tower that unleashes a devastating lightning storm. My personal favorite was the Temporal tower, which sends out a pulsing shock wave every few seconds, slowing down any enemies caught in each blast.

The trick to Defense Grid is that the goal isn’t just to wipe out the enemy or survive each wave — you’re trying to prevent them from stealing your power cores. Once an alien reaches your power station, it grabs between one and three cores, depending on its strength, and hightails it towards the exit. Kill them, and the power core they’re carrying will slowly float back to your power station. But if another enemy intercepts that floater, they’ll scoop it up, and make a beeline for the exit.

There are 20 maps in all, and to complete one, you have to survive all enemy waves with at least one power core still in your possession. Your final score is a tally of the remaining power cores, the value of the towers you’ve erected, and the total number of resources you’ve amassed.

The first few maps do a great job of easing you in: They’re simple, single path affairs, and there aren’t very many towers to choose from. A few levels later, and Defense Grid opens up entirely: you’ll suddenly find yourself herding angry alien sheep. Fortunately, an expanded arsenal and interesting mechanics will help turn the tide.

Each of your towers is surrounded by a force field, which the aliens dislike — it doesn’t hurt them, but they’d prefer to avoid it. You’ll have to erect your towers as a sort of fence, goading the aliens towards long, serpentine routes, to keep them in contact with your towers and delaying their advance to the power cores. Attempt to lock them into a dead end and they’ll just march right around your towers, taking the shortest routes and potentially circumventing your defenses altogether.

Proper tower placement will help make for an efficient alien-killing machine. Towers must have a line of sight to the enemy, so they can’t shoot through one another, but they’re also rather intelligent. Your towers will prioritize targets, ignoring empty-handed aliens and turning to focus on those carrying power cores, in order of the critters’ proximity to an exit. They’ll also coordinate attacks — place a few Temporal towers near each other, and each will time their pulses to prevent overlapping, slowing packs of enemies down for as long as possible.

Then there are the little touches. Simple visual cues — the colors green, yellow, and red — denote the strength of both enemies and towers. A quick button press will reveal the attack range of all of your towers, so you’ll know where you’re lacking coverage, while another will speed up the action if there’s a lull in the battle. Enemy waves and the composition of each strike scroll by on a ticker at the top of your screen, and there’s an in-game encyclopedia, should you forget what a particular symbol means or want to read up on particular alien’s weaknesses. And if you’ve made some horrible mistake and find yourself overrun, hitting the Backspace key will rewind your progress back to a previous wave, allowing you to go as far back as you need to refine your strategy.

While there are no multi-player options, there’s still quite a bit of competition to be had. Every level contains three medals, bronze, silver, and gold, which are awarded based on the number of resources and cores you amass by the end, and there are number of challenges to master — beating a level with only a specific type of turret, without ever upgrading, with a fixed number of resources, etc. The game will be available through Steam’s digital distribution service and Xbox Live Arcade, which will bring with it 58 different achievements and online leaderboards. You’ll also be able to get it through Direct2Drive. The best part of it all? Probably the price tag: $20.

While the game should run fine on a wide range of systems — I was told it’d run on a 1.8 GHz machine with 512 MB of RAM — graphics cards might be an issue, particularly with so many detailed units scampering around a map. I also noticed a graphical glitch in the menu once or twice, but with a few weeks of polish time still left before launch that’s probably just me getting a little nitpicky.

Defense Grid promises to combine clever mechanics and great visuals with a ton of replay value, at a bargin bin price. If you’re a fan of tower defense games, strategy games, or just hate aliens, tuck a twenty dollar bill someplace safe until it arrives on December 8.

Image: Hidden Path Entertainment

See Also: