Whew! At first I imagined Valve was offering a subscription based service for early access. Looks like they'll maintain their "do no evil" image!
yuastnav wrote on Mar 20, 2013, 16:55: Kerbal Space program also looked interesting (at least judging by this article from Christopher Livingston on PCGamer, guess I gotta try the demo).
If you have more than a passing interest in space, Kerbal Space Program is AMAZING. It's nice to see it hit Steam (in some form). You'll probably be hitting the Wiki and forums if you don't know what an apoapsis or periapsis are. It's such a rewarding experience to build your own rocket and payload, launch it into orbit, and land on the moon.