My favorite RTS, Command and Conquor, went for the superduper futuristic tangent with its latest sequal. I always liked C@C 2 red Alert, build hords of tanks and have at it!
That said I've always liked Star Craft and the sequal looks really good. I checked out the gameplay videos and the Zerg are really creepy looking when the swarm into an enemy base, reminds me of a bunch of bugs....creepy!