[quote name='kilm']It's like a lot of games. Easy to play and pick up, but really hard to master.[/QUOTE]
This is StarCraft in a nutshell. The original StarCraft's campaign has an excellent learning curve, but online play is
highly competitive. Blizzard is well aware of this, however, which is why the matchmaking system's in place for SC2.
[quote name='Brownjohn']I heard that the multiplayer matchmaking system is supposed to work well to match players of equal skill level.
I preorderded the game, but have very little interest in playing the standard multiplayer game. I liked the SP in the original, and I'm extremely excited to play all the mods that come out of the game.[/QUOTE]
What little I saw of the matchmaking during the beta wasn't bad. I didn't play for very long (because, well, see below), so it may have been polished up even more since then.
And I'm another one of those weirdoes who prefers single-player SC to multiplayer

Can't wait to dive into SC2's campaign!
Anyway, OP, Blizzard makes extremely polished, high-quality games, so you really can't go wrong with anything from them. If you still have doubts though, you might want to check out one of their previous RTSes. WarCraft III and StarCraft are both cheaper than SC2 and available in "Battle Chest" sets which include their respective expansions.