The list of official changes for OilRush 0.63 can be found on this forum page, but the major items come down to improving the artificial intelligence, changing unit limits, adding a time pressure mode, adding a siege mode, improving the engine performance, decreasing the memory consumption, fixing various glitches and crashes, get the game working on the Sony PlayStation 3, adding two new maps, adding new environmental options, fixing various visual bugs, and work has begun on voice-overs for the single-player campaign mode.
The latest official release date for OilRush was slated for June, but in a private discussion a few weeks back I heard there might be a delay. Based upon this late-May release of OilRush 0.63, I'd suspect they may indeed end up slipping on the June release date until later in the summer. However, that hasn't been officially confirmed yet.
Being from Unigine Corp, OilRush does offer a native Linux client atop this impressive game engine that offers stunning graphics and features. It can be ordered from the OilRush web-site for those looking to support this very Linux-friendly game studio. Since pre-orders began in early March, there's sadly been only 1471 pre-orders so far as of this afternoon. Linux users were commanding the early sales, but they have since taken down the OS statistics. A Mac OS X build of OilRush is also still forthcoming.