Yes, I am a big old dork, but I love video games. And in particular ones that require you to think (sometimes under stressful conditions). And this game haunted me. I only just now got it out of my system.
Defense Grid is another "tower defense" games, where you earn credits by killing the bad guys which allows you to build or upgrade more towers. The best of breed of these tower defense games has to be Toy Soldiers, but this one comes in a close second. DG throws in the kicker of periodically allowing you to you use a GDI Laser (or whatever you want to call it, basically a evil laser from the sky that requires time to recharge). Sounds simple, right?
About a dozen hours of gaming later I can assure it is not. I think I went to bed dreaming of this stuff until I got it right. Overall? 4/5 stars. Definitely a good way to spend some time.