If you can't wait to get your hands on StarCraft 2: Legacy of the void, here's something that might tide you over. Modders have ported over the entirety of the original StarCraft campaign, and Brood War, into StarCraft 2. You'll need the Heart of the Swarm expansion, though if you're interested enough to go back and play the oldies I'd wager that you already own it.
You can find the download here, with a quick guide for how to install it.
The 'StarCraft: Mass Recall' mod even adds 3 maps that were 'hidden or deleted' from the main game, and 6 from the demo campaign that came out back in '98. I've never played either of them, but if they're anything like as good as the campaigns in their modern incarnations then they're worth a look.
The mod's actually been available for some time, though it's still being worked on continually. It's on version 5.4 now, with a patch just last week that fixed a bunch of bugs and jiggled some cutscenes around.
Legacy of the Void is out November 10.