I don't own this game, but have played it in school.  I haven't played the campaign missions, but have played multiplayer almost everyday for 2 months.  The graphics are dated, but that isn't where the fun is.  For me it is the fast paced-ness of the game that keeps me hooked.  Unlike most RTSs I have played, each misson doesn't have to take an hour and a half to complete.  If you know how to build, it can take you 5 minutes to defeat a game aginst a single computer opponent.  You can also build crazily, and go like that, or you can develop a strategy and either way, you stand a chance of winning.