I'm psyched up for Starcraft 2, even if I was never any good at the original. Perhaps second only to RPGs, RTS is one of my favorite genres when it comes to video games.
What popularized RTS, interestingly enough, was Dune II, a game based on Frank Herbert's Dune (and what's interesting is that it was a compelling video-game adaptation of a popular franchise). What got me into RTS, however, was the original Warcraft (in fact, my first taste of it was a demo game that came along with PC magazines).
Now as much as I love Warcraft, the problem with it (and a problem many other RTS games faced at the time) is that virtually each side was a carbon copy of the other. In Street Fighter, it's like Ryu fighting Ken. Aesthetics and flavor-wise, they're different but functionality-wise, they're clones of each other. Which is fine as far as game balance is concerned but when it comes to variety, there's so much more that can be explored.
Warcraft 2 was a step in the right direction. There were variations between the units but for the most part, both races worked the same. The clincher, however, was Starcraft. The game introduced three distinct races that vastly differed from its RTS predecessors. I mean you had the Zerg which bred like crazy yet it didn't follow the standard formula of "peasants" building/repairing a building--the Zerg actually transformed into them and was capable of regeneration. The Protoss, on the other hand, could build several structures using the same peasant and had shields as hit points. But most of all, each race had different units: The Terrans had marines (all-around versatile unitst), the Zerg had zerglings (weak but cheap, numerous melee units), and the Protoss had zealots (strong but expensive melee units).
Warcraft 3, in many ways, was simply a copy of Starcraft. That's not to say it didn't have its own innovative features (the Undead faction could "unsummon" buildings, the Night Elf buildings could move and attack units) but a lot of elements was taken from Starcraft and infused with various RPG influences. Of course to me, Warcraft 3 was really the transition from RTS to MMORPG.
Currently, Blizzard owns arguably two of the most popular RTS franchises: Warcraft and Starcraft. I mean the only other franchises that probably comes close is Command & Conquer and Civilization. Yet the one thing Blizzard manages to execute perfectly is that they innovate. Hopefully they'll come out on time. =) (Except this time, they were smart enough not to announce a date.)