Soviet Assault brings over the full single player campaign as featured in the original PC release, as well as adds in new missions played from the Soviet perspective. These additional missions will be packed in with the console versions, although PC players can pay a few bucks to download them as well.
Unfortunately, none of the new missions were shown; however, GameShark were told that most are reinterpretations of existing missions. In other words, don't expect new maps; instead, you take on the Soviet side in battles previously waged on the American front in the original campaign. To be sure, different objectives and units promise something new even if the missions themselves aren't exactly fresh.