About me: As a kid I played computer games way more than I like to admit, however lately I have about a week to finish a game before I get completly bored, that's why I stick to Blizzard games, they somehow always keep me interested.
I got a beta key on the first wave, in February (or was it January?). I've played a fair bit and was able to lodge myself in Platinum. So I play the campaign on Hard mode and I find it challenging enough. (Also, I have a wireless mouse and I'm playing on a 47'' TV, it's great for FPS games, not so great for RTS)
=======================
The Good
SC2 has finaly made women obselete
The multiplayer is great, everyone knows that so I'll skip to the Singleplayer campaign, I just can't get enough of it.
For one thing, the design of the missions is far, far better than that of starcraft one.
With almost every mission in SC1, the objective was the following:
A. Build your base
B. Blow up their's
There were a few twists here and there but every mission had pretty much the same layout. I'm not saying it's a bad thing, the game came out over 10 years ago when developpers were still figuring out how to make a good game. I'm saying SC2 is EVEN BETTER because every mission is unique in one fashion or another. So far my favorite is the zombie mission (you know the one

In Warcraft 3, most missions were the same, about blowing up the enemy base but because of creeping and the hero system, side quests were abundant. In SC2 they took a different route.
On top of the better mission design, you have dialogue with characters between missions and you can check out different areas of your ship for upgrades and whatnot. I don't know about you guys but I enjoy the 5-10 minute break between missions to just chill and figure out where to spend my credits. I'm more on the casual side of gaming so I like to take my time and really enjoy the game (Incidently, I chew slowly when I eat tasty food). By the way, the unit gallery in the armory is freaking cool!!
I also really enjoy how depending on which mission you complete first, you will have access to different units in another mission. This whole aspect give a strong RPG feel and prevents this RTS from becoming repetitve, which in my opinion, is the greatest downside of any RTS game.
Build a base
Build an army
Blow up your enemies
=======================
The Bad
Since nothing in this world is perfect, we try our best.
I did notice the script was bland in a few places. In the release trailer, you see a short conversation between Raynor and Prince Valerie and I swear, I heard those lines in about 10 different movies.
Raynor: Give me one reason why I shouldnt kill you!
Prince: I can offer you that which you have always wanted!
Raynor: You can get me a lifetime membership at Tarsonis Brewries!?
There's also the usual ''Your sacrifice will not have been in vain'' later on the in game.
Cliché lines aside, the voice actress for Dr. Hanson did a poor job in some places but I don't think I would have noticed so quickly if someone on the TL forums hadnt pointed it out first.
Point of Note: I played SC1 when I was a kid, and Warcraft 3 when I was a teenager, so now that I'm a fully grown adult I have higher standards for scripting and voice acting.
However, something seems to be missing. I played the Warcraft and SC campaigns many times over and I never noticed anything bad with the plot/script/acting. Moreover, the story was very immersive from the start while in SC2, I don't really care about the characters, or I don't beleive them. Or something...
Lastly, after seeing Blizzard talk about their map editor so much, I'm a bit dissapointed that they didnt even include a SINGLE custom UMS map with their game.
=======================
Activision
Kotic sucks!
We all know of Activision's plot to make us pay 200$ in total for this game and right off the bat it sounds damn awful. However, keep in mind that there is a LOT more work put into SC2 than there ever was in SC1 and so far, I feel like I've gotten my money's worth.
The only thing that bugs me about that is that the hardest part is now done. For the Protoss and Zerg expansions, all they need to do is whip out the map editor and charge us another 60$ for a ''completely'' new game.
=======================
So, the game is awesome. If you don't look for flaws you will never find them. Just shut up and enjoy it.