Real Time Strategy Games boil down to a few basic characteristics. First, it is run without turns or pausing in the game clock. Second, almost all have top down or 3rd person point of view. Third, the are 3D or at a minimum have the feel of 3D. You can basically think of them as strategy games that lean towards tactics, have a much faster pace and action feel.
Empire Earth III. Wow... please do NOT buy that game. You'd have more fun setting your money on fire and putting it down your pants!
Several review sites gave their 2007 Strategy Game of the Year to World in Conflict I'm not convinced that it is that good, but for those who's budget isn't too thin it is a fun game.