Defense Grid sounds like just-another-tower game, because, well, it sort of is. Building, upgrading and killing are established ideas within the genre. But its little touches add to it, and give it more character than a free flash version. Enemies all boast different aesthetic features that all stick within the same sci-fi art style. Details like bulbous joints that jut out from the four-legged creepy-crawlies and a metal shell that obviously protects a tougher grunt lend more variety of the mutated dino-dogs who crave your cores.

The addition of medals adds a significant amount of longevity to the game, as you'll need to have a near-perfect run to earn the top rank. You'll have to go the extra mile to ensure that exactly zero cores are stolen, and that every enemy is liquefied before it can so much as look at your precious, priceless orbs. It's a brilliant mechanic that will constantly keep you coming back to improve and perfect your run of a particular stage. Whether it's sacrificing laser tower-power for machine gun shield-breaking, or creating lengthy paths by blocking routes with structures, there's no shortage of strategy to be had in the six-to-eight hour campaign. The inclusion of unlocking ludicrously difficult and laughably simple difficulties also gives you more bang for your buck, especially if you're looking for a more challenging (or, if you're not such a great player, easier) approach to each of the 20 Levels, or wish to ease a newcomer in to the game. It's a bummer that these options aren't available until you've cleared the respective stage, but their inclusion certainly changes the pace of the well-balanced defense sim.

Defense Grid is a solid, well-rounded strategy game that expands on a few fundamental ideas. The slow pace allows for accessibility, but it heats up enough to sate the lust of tower defense-addicts everywhere with a steadily increasing challenge, tougher difficulties, and gold-medal awards that will drive perfectionists up the wall. Though the story is basically useless, the inclusion of a depressed computer to talk you through the waves of baddies keeps things entertaining as well as interesting. It's not entirely original, but it's hard to resist its razor-sharp hooks.

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