Defense Grid is a tower defense game, and at its core it's about what you'd expect for a game in the genre. You have a resource to protect, an invader that wants to take the resource, a few paths that the invaders can use to get to the resource, and defensive towers that you can build to stop them. Defense Grid doesn't mess with this formula, which is a good thing because the reason you see so many tower defense games these days is that it's a fun formula. What Defense Grid does do is take the basics and build upon them. There are many different types of invaders, aliens in this case, and you'll need to deal with them in different ways from the game's expansive arsenal of tower types. The result is a fun and challenging tower defense game which offers a bit more strategic depth than typical.

In Defense Grid the resource that you must protect is power cores. The aliens that want to steal your cores will enter the map and travel down the paths that lead to your cores in an effort to grab them and then carry them back off of the map. If they should manage to steal your last core, then all is lost and you lose the game. To stop them from taking your cores, you need to set up a gauntlet of defense towers bristling with weapons to stop them in their tracks. Since the aliens need to take the cores off of the map, your towers will actually have two chances to stop them, once on the way in and once on the way out. If you stop an alien carrying a core, then the core will automatically begin to make its way back to your stash. The only thing that you need to worry about is having the right towers deployed and in the right places.  While the original version of the game was developed for the PC to be controlled with the mouse, it has made the transition to XBLA nicely and placing and upgrading the towers is easily managed with the Xbox 360 controller.

Each level consists of several waves of attackers, but before each wave in unleashed you'll be able to see what type of alien that you'll be facing. This is important because there are a variety of aliens in the game and certain towers are more effective against some aliens than others. Have the wrong mix of towers in place you'll watch helplessly as the aliens go waltzing off of the map with your precious cores. It's not a simple matter of packing every square inch of available real estate with towers, though. You'll have a limited budget with which to purchase towers and of course the more powerful ones will cost you more than the basic machine gun towers. You can also pay to upgrade your existing towers to more powerful versions rather than spend that money on new towers. Money for your towers is earned by killing aliens, so the more efficiently you can kill them the quicker you can fill your coffers. Towers include lasers, artillery, Tesla coils, and a number of other ways to shoot, burn, and shoot the aliens, and the trick to the game is to select the optimum mix and placement that will quickly stop the next alien wave.

The game includes twenty different levels, and while the first few should be easily managed by most gamers the difficulty quickly ramps up. Twenty levels may not seem like a lot, but the odds are against you that you'll beat each one on your first try. Some of the difficulty is due to the fact that maps aren't all simple one or two path mazes. Some introduce multiple entrances and exits and others don't really have paths at all. On these types of maps you'll need to use some of your towers to define the paths that you want to force the aliens to take. Once you do complete the game, there's still replay value to be had. There are definitely wrong ways to approach each level, but there are also alternate strategies that can be successful. Since the game is not really a puzzle in which one set of towers placed in certain locations us required to complete a level, you can have fun replaying the levels and trying different strategies.  The XBLA version of the game includes both the original game released on Steam for the PC as well as the expansion pack, Borderlands, so you get an entire new set of levels to beat once you make it through the first set.

If you don't like tower defense games, then Defense Grid won't change your mind about the genre. However, if you do enjoy the occasional tower game or enjoy strategy games in general, Defense Grid is definitely worth your time.

In The End, This Game Hath Been Rated: 84%. There are a number of tower defense games out there, but Defense Grid is one of the better ones.