Jim tried valiantly to get us all to play this back in December, but unfortunately I suffer from a rare, tragic medical condition that means it takes at least three months to react to anything anyone says to me. Waitaminnit, Obama's president? And the Beatles have split? Man!
Grabbing it on a whim earlier this week, I've found it eating up a healthy whack of my spare time since. I'm feeling a little burnt-out on full-on strategy games, after losing myself in Dawn of War II, Empire: Total War, Men of War, Endwar (avoid) and Stormrise (avoid at all costs), but not yet quite ready for the warm front of action games due to hit from Summer onwards.
Defence Grid hits somewhere in the middle - it's a tower defence game, but blossomed into a full 3D game that leans far closer to RTS values than the average web-based tower offering does. Charmingly, it's also narrated by someone doing a Stephen Fry impression and blithering about raspberries -at least until the sheen of terribly English humour lifts to reveal past tragedies.
I'm concious I might simply echo Jim's thoughts, so I'll keep it brief. Essentially, it's the finest tower defence game I've yet played, with an expertly-balanced learning curve, plenty of variety of turrets, a satisfying sense of mega-death as you carve up all those trooping invaders with some impressively destructive big guns, and even a surprisingly engrossing storyline of sorts.
It remains a shame it's still $20/£13 rather than $10/£8ish, as I imagine that's quite the barrier to entry to gamers who feel they can get free tower defence from elsewhere at the drop of a hat. Definitely one to keep an eye out for should it ever drop in price - we'll let you know if it does in our weekly Bargain Bucket posts.
Oh, and if you've got an iPhone/iPod Touch, I can strongly recommend Fieldrunners for some super-slick handheld tower defence shenanigans.