For all that I'm generally not a big fan of straight RTS games, Homeworld is...different. Special, even. I didn't even play that much of the original game back when I owned it, but I still recognized there was something unique about it.
As for specifics... Despite being real-time, combat tends to be more tactical (due to taking place in a full 3D environment), and less of a twitch-fest. The visuals and artwork are stunning. The storyline is well done. The music is amazing. It has brought people to tears; how many strategy games (or even games in general) can say that?
Admittedly, I suspect Homeworld wouldn't have the same effect on most of us now, compared to what it might have two decades ago. Either way, though, the game definitely left its mark.