[Darkwind]

While we're on the subject of RTSs, I may as well mention Warcraft III. I've lost half a decade, maybe even closer to a full one, of my life to this game. I played it and only it (before discovering Dominions, obviously). I've never been good at real-time strategy (or any games really), but what kept me was the incredible editor. This one game can let you play a first-person shooter, an adventure game, a puzzler, or even turn-based maps. The editor is fairly simple--even I, in all of my under-10-years-old glory, dabbled at creating maps.