They were good games, unfortunately the online multiplayer for them is no longer available (unless they have some workaround for that now). The expansion to the first game was actually free originally, it was like $1.99 shipping and handling and they sent you the disc. And yes, they're unit-based RTS games, probably more similar to Company of Heroes or Myth than anything.
What's in the "special edition" for Ground Control 2 though? I only have the retail release and never heard of a special edition for the game.