HELL, IT'S ABOUT TIME.This game is awesome.
I've played 6 or 7 missions so far. I like the way they're given to you once you're on the Hyperion -- you can choose the order in which you complete the missions, but you still get to do them all in one playthrough (at least so far from what I've seen). I also love that you get plenty of units that aren't in the multiplayer, but make sense for the campaign. Old units like medics, firebats, and goliaths have made their way into the campaign, which adds a lot of welcome variety. Starcraft's problem was that the missions were too alike -- build an army, crush your opponents. There are way more things to do in SC2. I'll avoid spoilers for now, except to say that the day/night mission was completely awesome.
I also love the way you get upgrades, and this is where you actually do miss out on stuff, depending on what you decide to research and spend your credits on. During missions, you can complete optional objectives to gain "research points", like finding Protoss artifacts or killing unique Zerg creatures, and at each level of research you're forced to choose between two technologies. The one you don't pick is lost forever, so it makes each playthrough unique. You also get credits for completing each mission, and you can spend those on upgrades at the armory. Some are the same as the MP upgrades (except you spend credits on them instead of minerals and gas, and you have them at the start of every mission once you buy them), and some are completely new. Again, you don't have nearly enough credits to buy all the upgrades that are available, so you're always making judgement calls.
I've got plenty more to say, but that would cut into my playing time.
