I played SC2 at PAX and it was great [basically THE SAME GAME with new/different units and pretty graphics, so SC players please rest easy] . The game was pretty much almost done for all races, so the multiplayer should be there for all races immediately, I hope. I think by installments they're going to finish terran first, release it, work on zerg, release that, etc.
Installment or expansion, it's going to be full price. I remember paying $50 for Starcraft back in 1998 and then another $50 for Brood War! I never bought "Insurrection" though lol.
Also, in SC2, the Overlords shit creep. \m/