To be honest, Blizzard is possibly one of the best companies for creating RTS games. They seem to figure out the mistakes they made with each game as well as learning from the successes of other games. For that reason, I know that StarCraft 2 is likely to take the best elements of the RTS industry and improve upon them.
For example, their demonstration of the campaign for the game (I think you can find videos of it on Youtube). From details given in that demonstration, StarCraft 2 is going to be map-based, non-linear play with a very definite campaign. And, they're already making the three races even more distinct than they were in the original.
Also, someone brought up WoW earlier. I have played it. Remember the issues with Diablo 2 and class balance? Unfortunately, Blizzard hasn't learned from that mistake and they've repeated it.
It was a good game in its time, but its time is long past. Any RTS worth playing these days, IMO, has a map-based, non-linear campaign and more than three distinct factions.
I would recommend Dawn of War: Dark Crusade for you. You'll want the original Dawn of War and the expansion pack for it as well. You'll probably notice some similarities between some of the units in it and StarCraft. This is not a coincidence. It's pretty easy to identify the Warhammer 40k elements that were adapted to StarCraft. Isn't the first time that scifi items have been adapted for other uses, and it certainly won't be the last time either.
