Defense Grid: Borderland and Resurgance

Hidden Path, the makers of the killer premium tower defense game Defense Grid: The Awakening have released their Borderland expansion to Steam users for free — no need to do anything, it will download when Steam auto-patches it. Previously, this same set of 4 levels was available to 360 users for free, but it's brand new to the Steam version. I purchased Defense Grid at Steam on sale over the new year, and it was the best $2.50 I've spent in a long time — it would have been a deal at 10x the price. At this point, if they put the Defense Grid brand on a steaming pile of crap, I'd buy it. Just in case they knew something about steaming crap that I don't. My theory for game developers is a lot like my theory for authors, if they prove their quality, stick with them.

Hidden Path is also working on another expansion planned for April, called Defense Grid: Resurgence. There aren't many games I buy at full price, but I'll be picking up Resurgence the day it releases.

Spoiler alert. The following are links to videos of the 4 Borderland levels (presumeably from the 360 version, since they're dated 3 months ago). I haven't watched them since I haven't finished the levels yet, but best to assume they could ruin the fun of playing them for yourself. Avoid them unless you just can't help yourself.
Onslaught
Infiltration
Entanglement
Forge