I know I'm late to the party, but I've never gotten the "it's 1/3 of a game" argument. It has as much or more content as the other Starcraft releases.
Also, the way they've handled it is nothing like Diablo 2 where they outright stated that they hadn't finished the game and the rest would be available in an expansion. Having played Diablo 2 (and LoD) more than any other game in my life, I remember just how much better the balance felt with the expansion. Going from beating Diablo to starting Nightmare the first time without the expansion was a *****. THAT was an incomplete game that sold unfinished content as an expansion.
SC2 is nothing like that. It's not like your campaign gets cut off before you beat the final boss and get your actual ending. You get a complete story, and you get a complete multiplayer experience. And for people that like the game, it's worth way more than the $60 they paid for it.
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"Principally I hate and detest the animal called man, although I heartily love John, Peter, Thomas and so forth" - Jonathan Swift
BT with the victory!