The Steam launch is just Windows for now, next up is updated and shinier graphics to coincide with the Linux and Mac Steam versions of the game. Full AA, HDR bloom, dynamic soft shadows, all the stuff that nearly made it for the Windows-release.
After that, LAN-play is being worked on internally, but it’s far from being cooked yet, Steamworks support and Steam achievements etc.. will be due with that, and full 3D physics integration (for the gems, meteors etc..), so expect much more dynamic levels coming up!
Content-wise, expect additional missions and also new wave types and more defensive and offensive unit types. Some of the prototype levels that didn’t make it in for v1.0 included space waves, night missions, offensive mission types, as well as single-unit direct-control missions, interactive level elements, level construction & building elements and some additional enemy unit types which will be released when they work and are fun to play with.
Any bugs found along the way will also be ruthlessly and viciously splatted too!