Just picked this game up from the Steam store. Incredibly fun MP game. I haven't even tried the SP or COOP modes yet, simply because MP is such a blast. It's like Battlefield 2 and Tribes had a self-produced baby. My biggest complaint after about 6 hours of solid play time is the fact it uses GFWL.
To learn more about the game, check out this video that convinced me to buy it: http://youtu.be/4AB51xrqp9s
Anyone else playing? Add me on GFWL under "Solanatum", and we'll do a Greentooth squad!