If you haven't noticed yet, today's (or yesterday's) update brought a new free map, made by one of the Steel Storm users. The map/mission is titled Assault on fKd City and is located under User Generated Content in the main menu. The mission might be raw, but you can make it better and add co-op support if you wish.
In March Steel Storm was #1[news.softpedia.com] in Ubuntu Software Center. Last month the game was on the #2 spot[news.softpedia.com] (among all Ubuntu Linux apps, not just games). Still going strong, despite whatever some "kitties" say :P Not bad for 1 year old game eh ;)